Status

Current state: Under DiscussionAccepted

Discussion thread: here

JIRA: here

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• All non-assignment metadata as defined in the ConsumerGroupHeartbeatRequest such as the group ID, member ID, member epoch, instance ID, rack ID and rebalance timeout.

• The currently assigned active, standby and warm-up tasks. Each task is identified by a subtopology ID (which can be an arbitrary string in protocol for future extensibility, even though subtopologies are currently numbered) and a partition number.

• The process ID to identify multiple members running in the same process (i.e. the same Streams client).

• The user-defined endpoint to be used for running interactive queries.

• Topology metadata needed for creating internal topics and computing the assignment.

• The topology epoch, which is defined by the client, and will be 0 normallyby default. The epoch can be bumped by the client to deploy a new version of the topology metadata.

• For each task, the current sum of task changelog offsets and task changelog end offsets. These are used to determine whether a warm-up task is below acceptable.recovery.lag and can be used to optimize the assignment in the assignor. For more details on these offsets see "Cumulative task changelog offsets and task changelog end offsets" section below

• A flag to request shutdown of the whole application (only if the member epoch is the group leave epoch).

Group ID, member ID, member epoch, and instance ID (if defined by the client) are sent with each heartbeat request. Any other information that has not changed since the last heartbeat can be omitted, unless an error occurred.

...

The metadata sent to the broker via the heartbeat is persisted as a new record type in the __consumer_offsets topic and is part of the group coordinator state in subsequent requests. If one or more source topics or internal topics do not exist, the group will enter state NOT_READY  and will attempt to create any missing internal topics (see more details below). Only after the topology metadata is initialized and all source topics and internal topics exist, the group coordinator starts assigning tasks to the members of the group.

Topology updates

To avoid unintential unintentional topology updates or rollbacks, updating the broker-side topology after it has been initialized for a group requires bumping the client-side configuration topology.epoch, which defaults to 0. By default, whenever a Streams member joins the group with a topology that is different from the current topology of the streams group, and the topology epoch is not bumped, the group coordinator will respond with an error, indicating that the member is incorrectly updating the broker-side topology. 

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1. Source topics missing
   Condition: A source topic is missing or a source topic regex resolves to zero topics.
   Behavior: The group will enter/remain in state NOT_READY.  Heartbeat responses will indicate status MISSING_SOURCE_TOPICS .  In the status detail, we specify all missing source topics and all regular expressions matching zero topics.
2. Topics incorrectly partitionedSource topics inconsistent
   Condition: The source Some topics are inconsistentincorrectly partitioned, if two source topics are supposed to be copartitioned according to the topology, but in the current topic metadata on the broker, the number of partitions for the two topics is different.
   Behavior: The group will enter/remain in state NOT_READY.  Heartbeat responses will indicate status SOURCE_TOPICS_INCONSISTENT . In the status detail, we specify at least one inconsistency.Internal topics are inconsistent
   Condition: One or more internal topics are inconsistent, for example, they are not copartition despite being part of a copartition group, or the number of partitions in a changelog topic does not correspond to the maximal number of source topic partition for that subtopology.
   Behavior: The group will enter/remain in state NOT_READY.  Heartbeat responses will indicate status INTERNALINCORRECTLY_PARTITIONED_TOPICS_INCONSISTENT  . In the status detail, we specify at least one inconsistencyincorrectly partitioned topic.
3. Internal topics are missing
   Condition: One or more internal topics are missing.
   Behavior: If discovered during a heartbeat, the group coordinator will attempt to create the internal topics by sending a corresponding topic create request will be sent to the Kraft coordinator. There can only be one such request in-flight at a time, an appropriate back-off mechanism will be used to prevent too many attempts to create the topics. If the appropriate ACL for topic creation are not assigned to the principle executing the heartbeat, no such attempt will be made. The group will enter/remain in state NOT_READY .  Heartbeat responses will indicate status MISSING_INTERNAL_TOPICS. In the status detail, we specify whether an attempt to create the topics was made, whether and why a previous attempt failed, whether sufficient ACLs to create the topics are available.
4. Topic configuration mismatches
   If an internal topic exists, but does not have the same configuration as defined in the topology (all parameters of the topic beside number of partitions, that is, replication factor, retention time, etc.), this will be logged on the broker, but otherwise be ignored.

...

• The partition metadata for the group, which is tracked by the group coordinator, is the partition metadata of all input topics (i.e., user source topics and internal repartition topics we read from).

• The group epoch is bumped:

  • When a member joins or leaves the group.
  • When a member is fenced or removed from the group by the group coordinator.
  • When the partition metadata is updated. For instance when a new partition is added or a new topic matching the subscribed topics is created.
  • When a member with an assigned warm-up task reports a task changelog offset and task changelog end offset whose difference is less that than acceptable.recovery.lag.
  • When a member updates its topology metadata, rack ID, client tags or process ID. Note: Typically, these do not change within the lifetime of a Streams client, so this only happens when a member with static membership rejoins with an updated configuration.
  • When an assignment configuration for the group is updated.

...

• For active processing tasks, the cumulative task changelog end offset is the same as the cumulative task changelog offset

• For all restoring tasks (active, standby or warm-up), the cumulative end-offset is the sum of the last end offsets cached by the restore consumer. If an end offset of a topic partition is unknown, no end-offset is reported.

• For dormant standby tasks, no end-offset is reported.

...

• Active tasks are reconciled like topic partitions in the KIP-848 consumer group protocol, that is, for reconciling the target assignment, the reconciliation follows three phases:

  • The group coordinator first asks the member to revoke any active tasks that are not assigned to that member in the target assignment any more (if either no warmup tasks are used at all, or if the target member has a hot standby/warmup task), by removing those active tasks from the set of tasks sent to the member in the heartbeat response

  • The member must first confirm revocation of these active tasks by removing them from the set of active tasks sent in the heartbeat request

  • Now, active tasks will be incrementally assigned to the member. An active task is assigned as soon as no other client owns it anymore, that is, once the previous owner (if any) has confirmed the revocation of the corresponding active task.

• Standby and warm-up tasks are reconciled in parallel with active tasks, but following slightly different logic:

  • As for active tasks, standby and warm-up tasks removed from the members target assignment are removed from the assignment sent in the heartbeat response immediately, that is, with the next heartbeat. The member confirms the revocation of the tasks as soon as the state directory (or any other resource related to the task) is closed.

  • Newly assigned standby and warm-up tasks await that any member with the same processId owning that task (as active or standby) confirms revocation of the task by removing it from the corresponding set in a heartbeat response. That is, a task that is not an active task or a standby task on any other member with the same processId can be assigned immediately. Otherwise, it is assigned as soon as the blocking task is revoked. Target assignments that assign a task to two members with the same processId are invalid.

...

The possible states of the streams group are EMPTY, ASSIGNING, RECONCILING , STABLE, NOT_READY, DEAD. The states are similar as for consumer groups, but contain an extra stat NOT_READY, which is used when a group is not empty and has a topology set, but not all topics are present to start processing using the topology.

Global & Dynamic Group Configuration

We make core assignment options configurable centrally on the broker, without relying on each clients configuration. This allows tuning a streams group without redeploying the streams application. The three core assignment options will be introduced on the broker-side: acceptable.recovery.lag, num.warmup.replicas and , num.standby.replicas, and rack.aware.assignment.tags. They can be configured both globally on the broker, and dynamically for specific streams groups through the IncrementalAlterConfigs and DescribeConfigs RPCs. 

We store the last used assignment configuration in the group metadata on the broker. This way, we can detect if an assignment configuration is dynamically changed, and we can trigger reassignment immediately.

Online Migration from Online Migration from a Classic Consumer Group to a Streams Group

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Let's recapitulate how the classic rebalance protocol works in Streams. First, the consumers in a Streams client join or re-join the group with the JoinGroup API. The JoinGroup request contains the subscribed topics, the owned partitions, the generation ID, the Streams-specific subscription info, and some other fields. The Streams-specific subscription info contains the process ID of the Streams client, the owned active and standby tasks, the task offset sums, the user endpoints for Interactive Query, and some more fields. When all the consumers of the Streams clients of the Streams application have joined, the group coordinator picks a leader for the group out of the consumers and sends back the JoinGroup response to all the members of the group (i.e., consumers that joined). The JoinGroup response contains the member ID, the generation ID, and the member ID of the leader (to make the leader aware of leadership) as well as all the consumer and Streams-specific metadata about subscribed topics, owned partitions, tasks, etc. The leader uses the data in the JoinGroup response for computing the assignment. Second, all the members in the Streams clients collect their assignment—computed by the leader—by using the SyncGroup API. The leader sends the computed assignment with the SyncGroup request to the group coordinator, and the group coordinator distributes the assignment to the members through the SyncGroup response. In parallel, the members heartbeat with the Heartbeat API in order to maintain their session. The Heartbeat API is also used by the group coordinator to inform the members about an ongoing rebalance. All those interactions are synchronized on the generation of the group. It is important to note that the consumer does not make any assumption about the generation ID. It basically uses what it receives from the group coordinator. The classic rebalance protocol used in Streams supports two modes: Eager and Cooperative. In the eager mode, the consumer revokes all its partitions before rejoining the group during a rebalance. In the cooperative mode, the consumer does not revoke any partitions before rejoining the group. However, it revokes the partitions that it does not own anymore when it receives its new assignment and rejoins immediately if he it had to revoke any partitions.

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The member must set all the (top level) fields with the exception of RackId and InstanceId when it joins for the first time or when an error occurs (e.g. request timed out). Otherwise, it is expected to only fill in the fields which have changed since the last heartbeat.

{
  "apiKey": TBD,
  "type": "request",
  "listeners": ["broker"],
  "name": "

{
  "apiKey": TBD,
  "type": "request",
  "listeners": ["broker", "zkBroker"],
  "name": "StreamsGroupHeartbeatRequest",
  "validVersions": "0", // "0" in 4.2/4.3 release; bumped to "0-1" in 4.4 release
  "flexibleVersions": "0+",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
      "about": "The group identifier." },     
    { "name": "MemberId", "type": "string", "versions": "0+",
      "about": "The member ID generated by the streams coordinatorconsumer. The member ID must be kept during the entire lifetime of the memberstreams consumer process." },
      { "name": "MemberEpoch", "type": "int32", "versions": "0+",
      "about": "The current member epoch; 0 to join the group; -1 to leave the group; -2 to indicate that the static member will rejoin." },
    { "name": "InstanceIdEndpointInformationEpoch", "type": "stringint32", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "nullThe ifcurrent notendpoint providedepoch or of this client, represents the latest endpoint epoch this client received"},
    { "name": "InstanceId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "null if not provided or if it didn't change since the last heartbeat; the instance ID for static membership otherwise." },
    { "name": "RackId", "type": "string", "versions": "0+",  "nullableVersions": "0+", "default": "null",
      "about": "null if not provided or if it didn't change since the last heartbeat; the rack ID of the consumermember otherwise." },
    { "name": "RebalanceTimeoutMs", "type": "int32", "versions": "0+", "default": -1,
      "about": "-1 if it didn't change since the last heartbeat; the maximum time in milliseconds that the coordinator will wait on the member to revoke its partitionstasks otherwise." },

    { "name": "Topology", "type": "Topology", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "The topology metadata of the streams application. Used to initialize the topology of the group and to check if the topology corresponds to the topology initialized for the group. Only sent when memberEpoch = 0, must be non-empty. Null otherwise.",
      "fields": [
        { "name": "Epoch", "type": "int32", "versions": "0+",
          "about": "The epoch of the topology. Used to check if the topology corresponds to the topology initialized on the brokers." },
        { "name": "Subtopologies", "type": "[]Subtopology", "versions": "0+",
          "about": "The sub-topologies of the streams application.",
          "fields": [
            { "name": "SubtopologyId", "type": "string", "versions": "0+",
              "about": "String to uniquely identify the sub-topologysubtopology. Deterministically generated from the topology" },
            { "name": "SourceTopics", "type": "[]string", "versions": "0+",
              "about": "The topics the topology reads from." },
            { "name": "SourceTopicRegex", "type": "[]string", "versions": "0+",
              "about": "The regular expressions identifying topics the sub-topologysubtopology reads from." },
            { "name": "StateChangelogTopics", "type": "[]TopicInfo", "versions": "0+",
              "about": "The set of state changelog topics associated with this sub-topologysubtopology. Created automatically." },
            { "name": "RepartitionSinkTopics", "type": "[]string", "versions": "0+",
              "about": "The repartition topics the sub-topologysubtopology writes to." },
            { "name": "RepartitionSourceTopics", "type": "[]TopicInfo", "versions": "0+",
              "about": "The set of source topics that are internally created repartition topics. Created automatically." },
            { "name": "CopartitionGroups", "type": "[]CopartitionGroup", "versions": "0+",
              "about": "A subset of source topics that must be copartitioned.",
              "fields": [
                { "name": "SourceTopics", "type": "[]int16", "versions": "0+",
                  "about": "The topics the topology reads from. Index into the array on the subtopology level." },
                { "name": "SourceTopicRegex", "type": "[]int16", "versions": "0+",
                  "about": "Regular expressions identifying topics the subtopology reads from. Index into the array on the subtopology level." },
                { "name": "RepartitionSourceTopics", "type": "[]int16", "versions": "0+",
                  "about": "The set of source topics that are internally created repartition topics. Index into the array on the subtopology level." }
              ]}
          ]}
      ]
    },

    { "name": "ActiveTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Currently owned active tasks for this client. Null if unchanged since last heartbeat." },
    { "name": "StandbyTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Currently owned standby tasks for this client. Null if unchanged since last heartbeat." },
    { "name": "WarmupTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Currently owned warm-up tasks for this client. Null if unchanged since last heartbeat." },

    { "name": "ProcessId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Identity of the streams instance that may have multiple consumers. Null if unchanged since last heartbeat." },
    { "name": "UserEndpoint", "type": "Endpoint", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "User-defined endpoint for Interactive Queries. Null if unchanged since last heartbeat or if not defined on the client." },
    { "name": "ClientTags", "type": "[]KeyValue", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Used for rack-aware assignment algorithm. Null if unchanged since last heartbeat." },

    { "name": "TaskOffsets", "type": "[]TaskOffset", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Cumulative changelog offsets for tasks. Only updated when a warm-up task has caught up, and according to the task offset interval. Null if unchanged since last heartbeat." },
    { "name": "TaskEndOffsets", "type": "[]TaskOffset", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Cumulative changelog end-offsets for tasks. Only updated when a warm-up task has caught up, and according to the task offset interval. Null if unchanged since last heartbeat." },
    { "name": "ShutdownApplication", "type": "bool", "versions": "0+", "default": false,
      "about": "Whether all Streams clients in the group should shut down." }
  ],

  "commonStructs": [
    { "name": "KeyValue", "versions": "0+", "fields": [
      { "name": "Key", "type": "string", "versions": "0+",
        "about": "key of the config" },
      { "name": "Value", "type": "string", "versions": "0+",
        "about": "value of the config" }
    ]},
    { "name": "TopicInfo", "versions": "0+", "fields": [
      { "name": "Name", "type": "string", "versions": "0+",
        "about": "The name of the topic." },
      { "name": "Partitions", "type": "int32", "versions": "0+",
        "about": "The number of partitions in the topic. Can be 0 if no specific number of partitions is enforced. Always 0 for changelog topics." },
      { "name": "ReplicationFactor", "type": "int16", "versions": "0+",
        "about": "The replication factor of the topic. Can be 0 if the default replication factor should be used." },
      { "name": "TopicConfigs", "type": "[]KeyValue", "versions": "0+",
        "about": "Topic-level configurations as key-value pairs."
      }
    ]},
    { "name": "Endpoint", "versions": "0+", "fields": [
      { "name": "Host", "type": "string", "versions": "0+",
        "about": "host of the endpoint" },
      { "name": "Port", "type": "int32uint16", "versions": "0+",
        "about": "port of the endpoint" }
    ]},
    { "name": "TaskOffset", "versions": "0+", "fields": [
      { "name": "SubtopologyId", "type": "string", "versions": "0+",
        "about": "The subtopology identifier." },
      { "name": "Partition", "type": "int32", "versions": "0+",
        "about": "The partition." },
      { "name": "Offset", "type": "int64", "versions": "0+",
        "about": "The offset." }
    ]},
    { "name": "TaskIds", "versions": "0+", "fields": [
      { "name": "SubtopologyId", "type": "string", "versions": "0+",
        "about": "The subtopology identifier." },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "The partitions of the input topics processed by this member." }
    ]}
  ]
}

...

• READ on group

• CREATE on cluster resource, or CREATE on all topics in StateChangelogTopics and RepartitionSourceTopics

  • Note that this ACLs are only required if the group coordinator should create the internal topics implicitly. If the internal topics are created explicitly, this ACL is not needed for the Streams group heartbeat.

• DESCRIBE_CONFIGS on  on all topics included in the message

...

• GroupId must be non-empty.

• Either MemberId is must be non-empty or MemberEpoch is 0.

• MemberEpoch must be >= -2.

• InstanceId, if not null, must be non-empty.

• RebalanceTimeoutMs must be larger than zero in the first heartbeat request.

• ActiveTasks, StandbyTasks and WarmupTasks have to be disjoint setsEach element of ActiveTasks, StandbyTasks and WarmupTasks has to be a valid task ID in the topology initialized for the group ID.

• ActiveTasks, StandbyTasks and WarmupTasks have to be non-null and empty when joining (member epoch is 0)

• If MemberEpoch  is 0, Topology should be non-null. Otherwise, it should be null.

...

1. Performs request validation.

2. If the member joins the group (i.e. member epoch is 0):

   1. Look up or create the group.
      1. If the group is created the topology epoch of the group is set to the topology epoch sent by the member.
   2. GROUP_ID_NOT_FOUND is returned if the group ID is associated with a group type that is not streams or classic (the latter will be allowed for migration).
   3. Compare the topology epoch of the request ER to the topology epoch of the group EG
      1. If ER=EG, check if topology metadata in the request is equal to the topology metadata of the group, otherwise fail with STREAMS_INVALID_TOPOLOGY_EPOCH
      2. If ER<EG, fail with STREAMS_TOPOLOGY_FENCED 
      3. If ER>EG+1, fail with STREAMS_INVALID_TOPOLOGY_EPOCH
      4. If ER=EG+1, update the topology by write riting the new topology record to the offset topic
   4. Creates the member.
3. If the member is already part of the group (i.e. member epoch is greater than 0):
   1. Looks up the group.
   2. GROUP_ID_NOT_FOUND is returned if the group ID does not exist anymore.
   3. If the member does not exist, returns UNKNOWN_MEMBER_ID
   4. Checks whether the member epoch matches the member epoch in its current assignment. FENCED_MEMBER_EPOCH is returned otherwise. The member is also removed from the group.
      • There is an edge case here. When the group coordinator transitions a member to its target epoch, the heartbeat response with the new member epoch may be lost. In this case, the member will retry with the member epoch that it knows about and its request will be rejected with a FENCED_MEMBER_EPOCH. This will be handled as in KIP-848.
   5. If the topology epoch in the request is less than the topology epoch of the group, set state STALE_TOPOLOGY  in the response.
4. Updates information of the member if needed. The group epoch is incremented if there is any change.
5. If the topology or topic metadata changed, detect any topology / topic mismatches as described earlier in this document.
6. Reconcile the member assignments as explained earlier in this document.

...

1. When a member assignment gets changed it will bump the StreamsGroup EndpointEpoch  and bump the corresponding member EndpointInformationEpoch in the response.  When all members EndpointInformationEpoch values converge on the same value as the group-wide EndpointEpoch updated IQ information will be included in the member heartbeat response.  

Response Schema

The group coordinator will only set the ActiveTasks, StandbyTasks and WarmupTasks fields until the member acknowledges that it has converged to the desired assignment. This is done to ensure that the members converge to the target assignment.

{
  "apiKey": TBD,
  "type": "response",
  "name": "StreamsGroupHeartbeatResponse",
  "

{
  "apiKey": TBD,
  "type": "response",
  "name": "StreamsGroupHeartbeatResponse",
  "validVersions": "0",  // "0" in 4.2/4.3 release; bumped to "0-1" in 4.4 release 
   "flexibleVersions": "0+",
  // Supported errors:
  // - GROUP_AUTHORIZATION_FAILED (version 0+)
  // - GROUP_ID_NOT_FOUND (version 0+)
  // - NOT_COORDINATOR (version 0+)
  // - COORDINATOR_NOT_AVAILABLE (version 0+)
  // - COORDINATOR_LOAD_IN_PROGRESS (version 0+)
  // - INVALID_REQUEST (version 0+)
  // - UNKNOWN_MEMBER_ID (version 0+)
  // - FENCED_MEMBER_EPOCH (version 0+)
  // - UNRELEASED_INSTANCE_ID (version 0+)
  // - GROUP_MAX_SIZE_REACHED (version 0+)
  // - TOPIC_AUTHORIZATION_FAILED (version 0+) 
  // - CLUSTER_AUTHORIZATION_FAILED (version 0+)
  // - STREAMS_INVALID_TOPOLOGY (version 0+)
  // - STREAMS_INVALID_TOPOLOGY_EPOCH (version 0+)
  // - STREAMS_TOPOLOGY_FENCED (version 0+)
  "fields": [
    // Same as consumer group heart beat
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "ErrorCode", "type": "int16", "versions": "0+",
      "about": "The top-level error code, or 0 if there was no error" },
    { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "The top-level error message, or null if there was no error." },      
    { "name": "MemberId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "The member id is always generated by the coordinator. Only provided when the member joins with MemberEpoch == 0." },streams consumer."},     
    { "name": "MemberEpoch", "type": "int32", "versions": "0+",
      "about": "The member epoch." },

    { "name": "HeartbeatIntervalMs", "type": "int32", "versions": "0+",
      "about": "The heartbeat interval in milliseconds." },
    { "name": "AcceptableRecoveryLag", "type": "int32", "versions": "0+",
      "about": "The maximal lag a warm-up task can have to be considered caught-up." },  // incorrectly implemented as `int32` in 4.2 release; updated to `int64` and request/response version bump to "1" in 4.4 release.
    { "name": "TaskOffsetIntervalMs", "type": "int32", "versions": "0+",
      "about": "The interval in which the task changelog offsets on a client are updated on the broker. The offsets are sent with the next heartbeat after this time has passed." },

    { "name": "Status", "type":  "[]Status", "versions":  "0+",  "nullableVersions": "0+", "default": "null",
      "about": "Indicate zero or more status for the group.  Null if unchanged since last heartbeat." },

    // The streams app knows which partitions to fetch from given this information
    { "name": "ActiveTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Assigned active tasks for this client. Null if unchanged since last heartbeat." },
    { "name": "StandbyTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Assigned standby tasks for this client. Null if unchanged since last heartbeat." },
    { "name": "WarmupTasks", "type": "[]TaskIds", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Assigned warm-up tasks for this client. Null if unchanged since last heartbeat." },

    // IQ-related information
    { "name": "EndpointInformationEpoch", "type": "int32", "versions": "0+",
      "about": "The endpoint epoch set in the response"}, 
    { "name": "PartitionsByUserEndpoint", "type": "[]EndpointToPartitions", "versions": "0+", "nullableVersions": "0+", "default": "null",
      "about": "Global assignment information used for IQ. Null if unchanged since last heartbeat." ,
      "fields": [
        { "name": "UserEndpoint", "type": "Endpoint", "versions": "0+",
          "about": "User-defined endpoint to connect to the node" },
        { "name": "PartitionsActivePartitions", "type": "[]TopicPartition", "versions": "0+",
          "about": "All active partitions available on the node" },
      ]
    }
  ],
  "commonStructs{ "name": [
    { "name"StandbyPartitions", "type": "Status[]TopicPartition", "versions": "0+", "fields": [
      // Possible status codes
      //   "about": "All standby paritions available on the node"}
      ]
    }
  ],
  "commonStructs": [
    { "name": "Status", "versions": "0+", "fields": [
      // Possible status codes
      //  0 - STALE_TOPOLOGY                 - The topology epoch supplied is lower than the topology epoch for this streams group.
      //  1 - MISSING_SOURCE_TOPICS          - One or more source topics are missing or a source topic regex resolves to zero topics.
      //                                       Missing topics are indicated in the StatusDetail.
      //  2 - INCONSISTENTINCORRECTLY_SOURCEPARTITIONED_TOPICS   - One or more source topics are incorrectly inconsistentpartitioned, forthat exampleis, they are not copartitioncopartitioned despite being 
      //                                       part of a copartition group.
, or the number of partitions //in a changelog topic does not correspond
         //                      Inconsistent topics are indicated in the StatusDetail.
      //  3 - INCONSISTENT_INTERNAL_TOPICS -to Onethe ormaximal morenumber internalof topicssource aretopic inconsistent,partition for example, they are not copartition despite beingthat subtopology.
      //                                     part of a copartition group, or the number of partitions in a changelog topic does not correspond
      //                                     to the maximal number of source topic partition for that subtopology. 
      //                                     Inconsistent Incorrectly partitioned topics are indicated in the StatusDetail. 
      //  43 - MISSING_INTERNAL_TOPICS        - One or more internal topics are missing. 
      //                                       Missing topics are indicated in the StatusDetail. 
      //                                       The group coordinator will attempt to create all missing internal topics, if any errors occur during
      //                                       topic creation, this will be indicated in StatusDetail.
      //  54 - SHUTDOWN_APPLICATION           - A client requested the shutdown of the whole application.
      { "name": "StatusCode", "type": "int8", "versions": "0+",
//  5 - ASSIGNMENT_DELAYED          "about": "A code to- indicate No assignment was provided because assignment computation was delayed.
      //  6 - MISSING_CLIENT_TAGS            - (Response v1+ only) The GC is configured to use `client.tag.` for rack-aware standby task assignment, but the client does not provide this tag
      { "name": "StatusCode", "type": "int8", "versions": "0+",
        "about": "A code to indicate that a particular status is active for the group membership" },
      { "name": "StatusDetail", "type": "string", "versions": "0+",
        "about": "A string representation of the status." }
    ]},
    { "name": "TopicPartition", "versions": "0+", "fields": [
      { "name": "Topic", "type": "string", "versions": "0+",
        "about": "topic name" },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "partitions" }
    ]},
    { "name": "TaskIds", "versions": "0+", "fields": [
      { "name": "SubtopologyId", "type": "string", "versions": "0+",
        "about": "The subtopology identifier." },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "The partitions of the input topics processed by this member." }
    ]},
    { "name": "Endpoint", "versions": "0+", "fields": [
      { "name": "Host", "type": "string", "versions": "0+",
        "about": "host of the endpoint" },
      { "name": "Port", "type": "uint16", "versions": "0+",
        "about": "port of the endpoint" }
    ]}
  ]
}

...

{
  "apiKey": TBD,
  "type": "request",
  "listeners": ["broker", "zkBroker"],
  "name": "StreamsGroupDescribeRequest",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "GroupIds", "type": "[]string", "versions": "0+", "entityType": "groupId",
      "about": "The ids of the groups to describe" },
    { "name": "IncludeAuthorizedOperations", "type": "bool", "versions": "0+",
      "about": "Whether to include authorized operations." }
  ]
}

Required ACL

• DESCRIBE on the group resource

• DESCRIBE on all topics used in the group's topologyRead Group

Request Validation

INVALID_REQUEST is returned should the request not obey the schema definition.

INVALID_GROUP_ID is returned should the group ID be empty.

...

• Checks whether the group ids exists. If it does not, GROUP_ID_NOT_FOUND is returned. Similarly, it is returned if the group ID is associated with a group type that is not streams .

• Looks up the groups and returns the response.

Response Schema

{
  "apiKey": TBD,
  "type": "response",
  "name": "StreamsGroupDescribeResponse",
  "validVersions": "0",
  "flexibleVersions": "0+",
  // Supported errors:
  // - GROUP_AUTHORIZATION_FAILED (version 0+)
  // - NOT_COORDINATOR (version 0+)
  // - COORDINATOR_NOT_AVAILABLE (version 0+)
  // - COORDINATOR_LOAD_IN_PROGRESS (version 0+)
  // - INVALID_REQUEST (version 0+)
  // - INVALID_GROUP_ID (version 0+)
  // - GROUP_ID_NOT_FOUND (version 0+)
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "Groups", "type": "[]DescribedGroup", "versions": "0+",
      "about": "Each described group.",
      "fields": [
        { "name": "ErrorCode", "type": "int16", "versions": "0+",
          "about": "The describe error, or 0 if there was no error." },
        { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
          "about": "The top-level error message, or null if there was no error." },
        { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
          "about": "The group ID string." },
        { "name": "GroupState", "type": "string", "versions": "0+",
          "about": "The group state string, or the empty string." },
        { "name": "GroupEpoch", "type": "int32", "versions": "0+",
          "about": "The group epoch." },
        { "name": "AssignmentEpoch", "type": "int32", "versions": "0+",
          "about": "The assignment epoch." },

        { "name":  "Topology", "type": "Topology", "versions": "0+",
          "about"nullableVersions": "0+", "default": "null",
          "about": "The topology metadata currently initialized for the streams application. Can be null in case of a describe error.",
          "fields": [
            { "name": "Epoch", "type": "uint32int32", "versions": "0+",
              "about": "The epoch of the currently initialized topology for this group." },
            { "name": "Subtopologies", "type": "[]Subtopology", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "The subtopologies of the streams application. This contains the configured subtopologies, where the number of partitions are set and any regular expressions are resolved to actual topics. Null if the group is uninitialized, source topics are missing or incorrectly inconsistentpartitioned.",
              "fields": [
                { "name": "SubtopologyId", "type": "string", "versions": "0+",
                  "about": "String to uniquely identify the subtopology." },
                { "name": "SourceTopics", "type": "[]string", "versions": "0+",
                  "about": "The topics the subtopology reads from." },
                { "name": "RepartitionSinkTopics", "type": "[]string", "versions": "0+",
                  "about": "The repartition topics the subtopology writes to." },
                { "name": "StateChangelogTopics", "type": "[]TopicInfo", "versions": "0+",
                  "about": "The set of state changelog topics associated with this subtopology. Created automatically." },
                { "name": "RepartitionSourceTopics", "type": "[]TopicInfo", "versions": "0+",
                  "about": "The set of source topics that are internally created repartition topics. Created automatically." }
              ]}
          ]},
        { "name": "Members", "type": "[]Member", "versions": "0+",
          "about": "The members.",
          "fields": [
            { "name": "MemberId", "type": "string", "versions": "0+",
              "about": "The member ID." },
            { "name": "MemberEpoch", "type": "int32", "versions": "0+",
              "about": "The member epoch." },
  
            { "name": "InstanceId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "The member instance ID for static membership." },
            { "name": "RackId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "The rack ID." },

            { "name": "ClientId", "type": "string", "versions": "0+",
              "about": "The client ID." },
            { "name": "ClientHost", "type": "string", "versions": "0+",
              "about": "The client host." },

            { "name": "TopologyEpoch", "type": "uint32int32", "versions": "0+",
              "about": "The epoch of the topology on the client." },

            { "name": "ProcessId", "type": "string", "versions": "0+",
              "about": "Identity of the streams instance that may have multiple clients. " },
            { "name": "UserEndpoint", "type": "Endpoint", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "User-defined endpoint for Interactive Queries. Null if not defined for this client." },
            { "name": "ClientTags", "type": "[]KeyValue", "versions": "0+",
              "about": "Used for rack-aware assignment algorithm." },
            { "name": "TaskOffsets", "type": "[]TaskOffset", "versions": "0+",
              "about": "Cumulative changelog offsets for tasks." },
            { "name": "TaskEndOffsets", "type": "[]TaskOffset", "versions": "0+",
              "about": "Cumulative changelog end offsets for tasks." },

            { "name": "Assignment", "type": "Assignment", "versions": "0+",
              "about": "The current assignment." },
            { "name": "TargetAssignment", "type": "Assignment", "versions": "0+",
              "about": "The target assignment." },
          ]},
        { "name": "AuthorizedOperationsIsClassic", "type": "int32bool", "versions": "0+",
 "default": "-2147483648",
            "about": "32-bit bitfield to represent authorized operations for this groupTrue for classic members that have not been upgraded yet." }
         ]},
    }
   ],
 { "commonStructsname": [
    {"AuthorizedOperations", "nametype": "TaskOffsetint32", "versions": "0+", "fieldsdefault": [
"-2147483648",
         { "nameabout": "SubtopologyId", "type32-bit bitfield to represent authorized operations for this group." }
      ]
    }
  ],
  "commonStructs": [
    { "name": "stringEndpoint", "versions": "0+",
        "aboutfields": "The subtopology identifier." },[
      { "name": "PartitionHost", "type": "int32string", "versions": "0+",
        "about": "The partition.host of the endpoint" },
      { "name": "OffsetPort", "type": "int64uint16", "versions": "0+",
        "about": "The offset.port of the endpoint" }
    ]},
      { "name": "TopicPartitionsTaskOffset", "versions": "0+", "fields": [
      { "name": "TopicIdSubtopologyId", "type": "uuidstring", "versions": "0+",
        "about": "The topicsubtopology IDidentifier." },
      { "name": "TopicNamePartition", "type": "stringint32", "versions": "0+", "entityType": "topicName",
        "about": "The topic namepartition." },
      { "name": "PartitionsOffset", "type": "[]int32int64", "versions": "0+",
        "about": "The partitionsoffset." }
    ]},
    { "name": "AssignmentTopicPartitions", "versions": "0+", "fields": [
      { "name": "ActiveTasksTopicId", "type": "[]TaskIdsuuid", "versions": "0+",
        "about": "ActiveThe tasks for this clienttopic ID." },
      { "name": "StandbyTasksTopicName", "type": "[]TaskIdsstring", "versions": "0+", "entityType": "topicName",
        "about": "StandbyThe tasks for this clienttopic name." },
      { "name": "WarmupTasksPartitions", "type": "[]TaskIdsint32", "versions": "0+",
        "about": "Warm-up tasks for this client. The partitions." }
    ]},
    { "name": "TaskIdsAssignment", "versions": "0+", "fields": [
      { "name": "SubtopologyIdActiveTasks", "type": "string[]TaskIds", "versions": "0+",
        "about": "The subtopology identifierActive tasks for this client." },
      { "name": "PartitionsStandbyTasks", "type": "[]int32TaskIds", "versions": "0+",
        "about": "Standby tasks for this client." },
      { "name": "The partitions of the input topics processed by this member."WarmupTasks", "type": "[]TaskIds", "versions": "0+",
        "about": "Warm-up tasks for this client. " }
    ]},
    { "name": "KeyValueTaskIds", "versions": "0+", "fields": [
      { "name": "KeySubtopologyId", "type": "string", "versions": "0+",
        "about": "keyThe of the configsubtopology identifier." },
      { "name": "ValuePartitions", "type": "string[]int32", "versions": "0+",
        "about": "valueThe partitions of the config" }
    input topics processed by this member." }
    ]},
    { "name": "KeyValue", "versions": "0+", "fields": [
      { "name": "Key", "type": "string", "versions": "0+",
        "about": "key of the config" },
      { "name": "Value", "type": "string", "versions": "0+",
        "about": "value of the config" }
    ]},
    { "name": "TopicInfo", "versions": "0+", "fields": [
      { "name": "Name", "type": "string", "versions": "0+",
        "about": "The name of the topic." },
      { "name": "Partitions", "type": "int32", "versions": "0+",
        "about": "The number of partitions in the topic. Can be 0 if no specific number of partitions is enforced. Always 0 for changelog topics." },
      { "name": "TopicConfigsReplicationFactor", "type": "[]KeyValueint16", "versions": "0+",
        "about": "Topic-level configurations as key-value pairsThe replication factor of the topic. Can be 0 if the default replication factor should be used." },
      { "name": "TopicConfigs", "type": "[]KeyValue", "versions": "0+",
        "about": "Topic-level configurations as key-value pairs."
      }
    ]}
  ]
}

Response Handling

...

• The member metadata record, keyed by the group ID and the member ID, stores all relevant metadata that is sent by a member to the coordinator in a heartbeat request. A notable exception are task changelog offsets and task changelog end offsets, which are not persisted, as they are constantly changing. 
• The group metadata, keyed by the group ID, contains the group epoch.
  • The group epoch
  • A hash of the topology metadata
  • The epoch of the last validated topology
  • The last configuration used by the assignor

The records evolve in the following way:

...

{
  "type": "data",
  "name": "StreamsGroupMemberMetadataValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "InstanceId", "versions": "0+", "nullableVersions": "0+", "type": "string",
      "about": "The (optional) instance ID for static membership." },
    { "name": "RackId", "versions": "0+", "nullableVersions": "0+", "type": "string",
      "about": "The (optional) rack id." },
    { "name": "ClientId", "versions": "0+", "type": "string",
      "about": "The client id." },
    { "name": "ClientHost", "versions": "0+", "type": "string",
      "about": "The client host." },
    { "name": "RebalanceTimeoutMs", "type": "int32", "versions": "0+", "default": -1,
      "about": "The rebalance timeout." },

    { "name": "TopologyEpoch", "type": "uint32int32", "versions": "0+",
      "about": "The epoch of the topology. Must be non-zero." },

    { "name": "ProcessId", "type": "string", "versions": "0+",
      "about": "Identity of the streams instance that may have multiple consumers." },
    { "name": "UserEndpoint", "type": "Endpoint", "versions": "0+",
      "nullableVersions": "0+", "default": "null",
      "about": "User-defined endpoint for running interactive queries on this instance." },
    { "name": "ClientTags", "type": "[]KeyValue", "versions": "0+",
      "about": "Used for rack-aware assignment algorithm." }
  ],
  "commonStructs": [
    { "name": "Endpoint", "versions": "0+", "fields": [
      { "name": "Host", "type": "string", "versions": "0+",
        "about": "host of the endpoint" },
      { "name": "Port", "type": "int32uint16", "versions": "0+",
        "about": "port of the endpoint" }
    ]},
    { "name": "KeyValue", "versions": "0+",
      "fields": [
        { "name": "Key", "type": "string", "versions": "0+",
          "about": "key of the config" },
        { "name": "Value", "type": "string", "versions": "0+",
          "about": "value of the config" }
      ]
    }
  ]
}

...

{
  "type": "data",
  "name": "StreamsGroupMetadataKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": TBD,
      "about": "The group id." }
  ]
}

StreamsGroupMetadataValue

...

{
  "type": "data",
  "name": "StreamsGroupMetadataValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "Epoch", "versions": "0+", "type": "int32",
      "about": "The group epoch." },
  ]
}

Group Topology Metadata

The topology for the group, and the metadata for input topic partitions consumed in the topology, are persisted in two records.

• The partition metadata record, keyed by the group ID, contains metadata of all topic partitions consumed by the current topology
• The topology record, keyed by the group ID, stores the topology metadata sent in the heartbeat request when members join.

The records are evolved in the following way

• When the group coordinator receives valid topology metadata in a heartbeat request, both records are created, using the topology sent in the request and the topic metadata currently known to the group coordinator.
• When the group coordinator detects that the partition metadata for one of the input partitions used in the topology changed (by comparing the previous partition metadata record to the currently known topic metadata in the broker) during the handling of a group heartbeat, the stream group partition metadata record is updated, and a new assignment is computed.

When the group lost all members and offsets.retention.minutes expires, tombstones is written to remove the records.

StreamsGroupPartitionMetadataKey

{
  "type": "data",
  "name": "StreamsGroupPartitionMetadataKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": TBD,
      "about": "The group id." }
  ]
}

StreamsGroupPartitionMetadataValue

{
  "type": "data",
  "name": "StreamsGroupPartitionMetadataValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields"    { "name": "MetadataHash", "versions": "0+", "type": "int64",
      "about": "The hash of all topics in the group." },
    { "name": "ValidatedTopologyEpoch", "versions": "0+", "taggedVersions": "0+", "tag": 0, "default": -1, "type": "int32",
      "about": "The topology epoch whose topics are validated to be present in a valid configuration in the metadata." },
    { "name": "LastAssignmentConfigs","taggedVersions": "0+", "nullableVersions": "0+","tag": 1, "default": null,
      "type": "[]LastAssignmentConfig", "about": "The last used configuration parameters as key-value pairs." }
  ],
  "commonStructs": [
    { "name": "TopicsLastAssignmentConfig", "versions": "0+", "type": "[]TopicMetadata",
      "about": "The list of topic metadata.", "fields": [
      { "name": "TopicIdKey", "versionstype": "0+string", "typeversions": "uuid0+",
        "about": "TheKey of topicthe idconfig." },
      { "name": "TopicNameValue", "versionstype": "0+string", "typeversions": "string0+",
        "about": "TheValue of topicthe nameconfig." },
      { "name": "NumPartitions", "versions": "0+", "type": "int32",
        "about": "The number of partitions of the topic." },
      { "name": "PartitionMetadata", "versions": "0+", "type": "[]PartitionMetadata",
        "about": "Partitions mapped to a set of racks. If the rack information is unavailable for all the partitions, an empty list is stored", "fields": [
      ]}
  ]
}

Group Topology Metadata

The topology for the group, and the metadata for input topic partitions consumed in the topology, are persisted in two records.

• The partition metadata record, keyed by the group ID, contains metadata of all topic partitions consumed by the current topology
• The topology record, keyed by the group ID, stores the topology metadata sent in the heartbeat request when members join.

The records are evolved in the following way

• When the group coordinator receives valid topology metadata in a heartbeat request, both records are created, using the topology sent in the request and the topic metadata currently known to the group coordinator.
• When the group coordinator detects that the partition metadata for one of the input partitions used in the topology changed (by comparing the previous partition metadata record to the currently known topic metadata in the broker) during the handling of a group heartbeat, the stream group partition metadata record is updated, and a new assignment is computed.

When the group lost all members and offsets.retention.minutes expires, tombstones is written to remove the records.

StreamsGroupPartitionMetadataKey

{
  "type": "data",
  "name": "StreamsGroupPartitionMetadataKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
    { "name": "PartitionGroupId", "versionstype": "0+string", "typeversions": "int32"TBD,
            "about": "The partitiongroup numberid." },
  ]
}

StreamsGroupPartitionMetadataValue

{
    "type": "data",
    { "name": "RacksStreamsGroupPartitionMetadataValue",
  "versionsvalidVersions": "0+",
  "typeflexibleVersions": "[]string0+",
            "aboutfields": "The set of racks that the partition is mapped to." }
      ]}[
    ]}
  ]
}

StreamsGroupTopologyKey

{
  "typename": "dataTopics",
  "nameversions": "StreamsGroupTopologyKey0+",
  "validVersionstype": TBD"[]TopicMetadata",
      "flexibleVersionsabout": "noneThe list of topic metadata.",
  "fields": [
      { "name": "GroupIdTopicId", "typeversions": "string0+", "versionstype": TBD"uuid",
        "about": "The grouptopic id." },
  ]
}

StreamsGroupTopologyValue

{
  "type    { "name": "dataTopicName",
  "nameversions": "StreamsGroupTopologyValue0+",
  "validVersionstype": "0string",
        "flexibleVersionsabout": "0+"The topic name." },
  "fields": [
    { "name": "EpochNumPartitions", "typeversions": "int0+", "versionstype": "0+int32",
        "about": "The epochnumber of thepartitions topology.of Must be non-zero. the topic." },
      { "name":  "SubtopologiesPartitionMetadata", "typeversions": "[]Subtopology0+", "versionstype": "0+[]PartitionMetadata",
        "about": "The sub-topologiesPartitions mapped to a set of racks. If the streams application.",
      rack information is unavailable for all the partitions, an empty list is stored", "fields": [
          { "name": "SubtopologyIdPartition", "typeversions": "string0+", "versionstype": "0+int32",
            "about": "StringThe to uniquely identify the subtopologypartition number." },
          { "name": "SourceTopicsRacks", "typeversions": "[]string0+", "versionstype": "0+[]string",
            "about": "The topics set of racks that the partition topologyis readsmapped fromto." },
      ]}
    ]}
  ]
}

StreamsGroupTopologyKey

{
  "nametype": "SourceTopicRegexdata",
  "typename": "[]stringStreamsGroupTopologyKey",
  "versionsvalidVersions": "0+"TBD,
          "about"flexibleVersions": "The regular expressions identifying topics the topology reads from." }none",
  "fields": [
     { "name": "StateChangelogTopicsGroupId", "type": "[]TopicInfostring", "versions": "0+"TBD,
      "about": "The group id." }
  ]
}

StreamsGroupTopologyValue

{
  "type"about": "data"The set of state changelog topics associated with this subtopology. " },
	,
  "name": "StreamsGroupTopologyValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "RepartitionSinkTopicsEpoch", "type": "[]stringint32", "versions": "0+",
          "about": "The repartitionepoch topicsof the sub-topology writes. to." }, 
        { "name":  "RepartitionSourceTopicsSubtopologies", "type": "[]TopicInfoSubtopology", "versions": "0+",
          "about": "The setsub-topologies of sourcethe topics that are internally created repartition topics. " }streams application.",
      "fields": [
        { "name": "CopartitionGroupsSubtopologyId", "type": "[]CopartitionGroupstring", "versions": "0+",
          "about": "AString subsetto ofuniquely sourceidentify topics that must be copartitionedthe subtopology." },
          "fields": [
            { "name": "SourceTopics", "type": "[]int32string", "versions": "0+",
              "about": "The topics the topology reads from. Index into the array on the subtopology level." },
            { "name": "SourceTopicRegex", "type": "[]int32string", "versions": "0+",
              "about": "Regular expressions identifying topics the subtopology reads from. Index into the array on the subtopology level." },
            { "name": "RepartitionSourceTopicsStateChangelogTopics", "type": "[]int32TopicInfo", "versions": "0+",
              "about": "The set of source topics that are internally created repartitionstate changelog topics. Indexassociated into the array on the subtopology levelwith this subtopology." },
        { "name": "RepartitionSinkTopics", "type": "[]string", "versions": "0+",
        }
      ]
    }
  ],
  "commonStructs": [
"about": "The repartition topics the subtopology writes to." },
        { "name": "TopicConfigRepartitionSourceTopics", "versionstype": "0+", "fields": [
      { "name": "key", "type": "string", "[]TopicInfo", "versions": "0+",
          "about": "The keyset of the topic-level configuration source topics that are internally created repartition topics." },
        { "name": "valueCopartitionGroups", "type": "string[]CopartitionGroup", "versions": "0+",
          "about": "TheA valuesubset of thesource topic-level configuration," }
    ]
topics that must be copartitioned.",
     },
    { "namefields": "TopicInfo", "versions": "0+", "fields": [
 [
            { "name": "NameSourceTopics", "type": "string[]int16", "versions": "0+",
              "about": "The name oftopics the topology reads from. Index into the array on the topicsubtopology level." },
            { "name": "PartitionsSourceTopicRegex", "type": "int32[]int16", "versions": "0+",
              "about": "TheRegular expressions numberidentifying oftopics partitionsthe insubtopology thereads topicfrom. CanIndex beinto 0the ifarray noon specificthe numbersubtopology of partitions is enforced. Always 0 for changelog topics." },
level." },
             { "name": "TopicConfigsRepartitionSourceTopics", "type": "[]TopicConfigint16", "versions": "0+", "nullableVersions": "0+", "default": "null",

              "about": "Topic-level configurations as key-value pairs."The set of source topics that are internally created repartition topics. Index into the array on the subtopology level." }
          ]
        }
      ]
    }
  ]
}

Current Member Assignment

For each member, there is a record to store the current member assignment. The record is first created when a member joins (with an empty assignment). Every time an assignment is computed for the member during reconciliation, it is compared to the previous assignment for the member. If the assignment changed, a new version of the current member assignment record is appended to the consumer offset topic. When the member leaves the group, a tombstone is written to remove the record.

StreamsGroupCurrentMemberAssignmentKey

{
  "type": "data",
  "name": "StreamsGroupCurrentMemberAssignmentKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
 ,
  "commonStructs": [
    { "name": "TopicConfig", "versions": "0+", "fields": [
      { "name": "GroupIdkey", "type": "string", "versions": TBD"0+",
        "about": "The group idkey of the topic-level configuration." },
      { "name": "MemberIdvalue", "type": "string", "versions": TBD"0+",
        "about": "The member id. value of the topic-level configuration," }
    ]
}

StreamsGroupCurrentMemberAssignmentValue

{    },
  "type": "data",
 { "name": "StreamsGroupCurrentMemberAssignmentValueTopicInfo",
  "validVersionsversions": "0+",
  "flexibleVersionsfields": "0+",
[
  "fields": [
    { "name": "MemberEpochName", "versionstype": "0+string", "typeversions": "int320+",
        "about": "The currentname member epoch that is expected from the member in the heartbeat requestof the topic." },
      { "name": "PreviousMemberEpochPartitions", "versionstype": "0+int32", "typeversions": "int320+",
        "about": "IfThe number of partitions in the lasttopic. epochCan bumpbe is0 lostif beforeno reachingspecific thenumber member,of thepartitions memberis willenforced. retryAlways with0 thefor previouschangelog epochtopics." },
      { "name": "StateReplicationFactor", "versionstype": "0+int16", "typeversions": "int80+",
        "about": "The member state. See StreamsGroupMember.MemberState for the possible valuesreplication factor of the topic. Can be 0 if the default replication factor should be used." },
      { "name": "ActiveTasksTopicConfigs", "versionstype": "0+[]TopicConfig", "typeversions": "[]TaskIds0+",
        "about": "CurrentlyTopic-level assignedconfigurations activeas tasks for this streams client." },key-value pairs."
    { "name  }
    ]}
  ]
}

Current Member Assignment

For each member, there is a record to store the current member assignment. The record is first created when a member joins (with an empty assignment). Every time an assignment is computed for the member during reconciliation, it is compared to the previous assignment for the member. If the assignment changed, a new version of the current member assignment record is appended to the consumer offset topic. When the member leaves the group, a tombstone is written to remove the record.

Together with the assignment, we track the epoch at which an active task was assigned. This helps with offset commit validation: We allow offset commits for partitions that belong to tasks in all epochs since the assignment epoch of the task. 

StreamsGroupCurrentMemberAssignmentKey

{
  "type": "StandbyTasksdata",
  "versionsname": "0+StreamsGroupCurrentMemberAssignmentKey",
  "typevalidVersions": "[]TaskIds"TBD,
      "aboutflexibleVersions": "Currentlynone",
 assigned standby tasks for this streams client." }, "fields": [
    { "name": "WarmupTasksGroupId", "versionstype": "0+string", "typeversions": "[]TaskIds"TBD,
      "about": "CurrentlyThe assigned warm-up tasks for this streams clientgroup id." },
    { "name": "ActiveTasksPendingRevocationMemberId", "versionstype": "0+string", "typeversions": "[]TaskIds"TBD,
      "about": "The active tasks that must be revoked by this membermember id." }
  ]
}

StreamsGroupCurrentMemberAssignmentValue

{,
  "commonStructstype": ["data",
  "name": "StreamsGroupCurrentMemberAssignmentValue",
 { "namevalidVersions": "TaskIds0",
  "versionsflexibleVersions": "0+",
  "fields": [
      { "name": "SubtopologyIdMemberEpoch", "typeversions": "string0+", "versionstype": "0+int32",
        "about": "The subtopology identifier current member epoch that is expected from the member in the heartbeat request." },
      { "name": "PartitionsPreviousMemberEpoch", "typeversions": "[]int320+", "versionstype": "0+int32",
        "about": "TheIf partitionsthe oflast theepoch inputbump topicsis lost processedbefore byreaching thisthe member." }
    ]}
  ]
}

Streams Group Target Assignment

The target assignment is stored in N + 1 records, where N is the number of members in the group. When a new target assignment is computed, the group coordinator will compare it with the current target assignment and only write the difference between the two assignments to the __consumer_offsets  partition. That also means if a member left the group, a corresponding tombstone record is written. The assignment must be atomic, so the group coordinator will ensure that all the records are written in a single batch, limiting the size to the maximum batch size (default 1MB), as in consumer groups. 

StreamsGroupTargetAssignmentMemberKey

{
  "type": "data",
 , the member will retry with the previous epoch." },
    { "name": "StreamsGroupTargetAssignmentMemberKeyState",
  "validVersionsversions": TBD"0+",
  "flexibleVersionstype": "noneint8",
      "fieldsabout": [
    "The member state. See StreamsGroupMember.MemberState for the possible values." },
    { "name": "GroupIdActiveTasks", "typeversions": "string0+", "versionstype": TBD"[]TaskIds",
      "about": "The group idCurrently assigned active tasks for this streams client." },
    { "name": "MemberIdStandbyTasks", "typeversions": "string0+", "versionstype": TBD"[]TaskIds",
      "about": "The member idCurrently assigned standby tasks for this streams client." },
  ]
}

StreamsGroupTargetAssignmentMemberValue

{
  "type  { "name": "dataWarmupTasks",
  "nameversions": "StreamsGroupTargetAssignmentMemberValue0+",
  "validVersionstype": "0[]TaskIds",
      "flexibleVersionsabout": "0+",
  "fields": [Currently assigned warm-up tasks for this streams client." },
    { "name": "ActiveTasksActiveTasksPendingRevocation", "versions": "0+", "type": "[]TaskIds",
      "about": "Currently assignedThe active tasks for that must be revoked by this streams clientmember." },
    { "name": "StandbyTasksStandbyTasksPendingRevocation", "versions": "0+", "type": "[]TaskIds",
      "about": "CurrentlyThe assigned standby tasks for that must be revoked by this streams clientmember." },
    { "name": "WarmupTasksWarmupTasksPendingRevocation", "versions": "0+", "type": "[]TaskIds",
      "about": "Currently assigned warm-up tasks forThe warmup tasks that must be revoked by this streams clientmember." }
  ],
  "commonStructs": [
    { "name": "TaskIds", "versions": "0+", "fields": [
      { "name": "SubtopologyId", "type": "string", "versions": "0+",
        "about": "The subtopology identifier." },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "The partitions of the input topics processed by this member." },
    ]}
  ]
}

StreamsGroupTargetAssignmentMetadataKey

{
  "typename": "dataAssignmentEpochs",
  "nameversions": "StreamsGroupTargetAssignmentMetadataKey0+",
  "validVersionsnullableVersions": TBD,
 "0+", "flexibleVersionstaggedVersions": "none0+",
  "fieldstag": [
    { "name": "GroupId"0, "type": "string[]int32", "versionsdefault": TBDnull,
        "about": "The groupepoch id." }
  ]
}

StreamsGroupTargetAssignmentMetadataValue

{
  "type": "data",
  "name": "StreamsGroupTargetAssignmentMetadataValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "AssignmentEpoch", "versions": "0+", "type": "int32",
      "about": "The assignment epoch." at which any partition was assigned to the member. Used to fence zombie commits requests. Of the same length as partitions. If null, all assignment epochs are considered to be equal to the member epoch." }
     ]}
  ]
}

Broker Metrics

The existing group metrics are extended to differentiate between streams groups and consumer groups and account for streams group states.

• Number of groups based on type of the protocol, where the list of protocols is extended by the protocol=streams variation.

kafka.server:type=group-coordinator-metrics,name=group-count,protocol={consumer|classic|streams}

• Number of streams groups based on state

kafka.server:type=group-coordinator-metrics,name=streams-group-count,state={empty|not_ready|assigning|reconciling|stable|dead}

• Streams group rebalances sensor

kafka.server:type=group-coordinator-metrics,name=streams-group-rebalance-rate

kafka.server:type=group-coordinator-metrics,name=streams-group-rebalance-count

Broker Configurations

The new group protocol would be guarded by enabling a new version of the group.version feature flag on the broker side.

Updated properties

New properties

Group Configurations

...

Streams Group Target Assignment

The target assignment is stored in N + 1 records, where N is the number of members in the group. When a new target assignment is computed, the group coordinator will compare it with the current target assignment and only write the difference between the two assignments to the __consumer_offsets  partition. That also means if a member left the group, a corresponding tombstone record is written. The assignment must be atomic, so the group coordinator will ensure that all the records are written in a single batch, limiting the size to the maximum batch size (default 1MB), as in consumer groups. 

StreamsGroupTargetAssignmentMemberKey

{
  "type": "data",
  "name": "StreamsGroupTargetAssignmentMemberKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": TBD,
      "about": "The group id." },
    { "name": "MemberId", "type": "string", "versions": TBD,
      "about": "The member id." }
  ]
}

StreamsGroupTargetAssignmentMemberValue

{
  "type": "data",
  "name": "StreamsGroupTargetAssignmentMemberValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "ActiveTasks", "versions": "0+", "type": "[]TaskIds",
      "about": "Currently assigned active tasks for this streams client." },
    { "name": "StandbyTasks", "versions": "0+", "type": "[]TaskIds",
      "about": "Currently assigned standby tasks for this streams client." },
    { "name": "WarmupTasks", "versions": "0+", "type": "[]TaskIds",
      "about": "Currently assigned warm-up tasks for this streams client." }
  ],
  "commonStructs": [
    { "name": "TaskIds", "versions": "0+", "fields": [
      { "name": "SubtopologyId", "type": "string", "versions": "0+",
        "about": "The subtopology identifier." },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "The partitions of the input topics processed by this member." }
    ]}
  ]
}

StreamsGroupTargetAssignmentMetadataKey

{
  "type": "data",
  "name": "StreamsGroupTargetAssignmentMetadataKey",
  "validVersions": TBD,
  "flexibleVersions": "none",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": TBD,
      "about": "The group id." }
  ]
}

StreamsGroupTargetAssignmentMetadataValue

{
  "type": "data",
  "name": "StreamsGroupTargetAssignmentMetadataValue",
  "validVersions": "0",
  "flexibleVersions": "0+",
  "fields": [
    { "name": "AssignmentEpoch", "versions": "0+", "type": "int32",
      "about": "The assignment epoch." }
  ]
}

Broker Metrics

The existing group metrics are extended to differentiate between streams groups and consumer groups and account for streams group states.

• Number of groups based on type of the protocol, where the list of protocols is extended by the protocol=streams variation.

kafka.server:type=group-coordinator-metrics,name=group-count,protocol={consumer|classic|streams}

• Number of streams groups based on state

kafka.server:type=group-coordinator-metrics,name=streams-group-count,state={empty|not_ready|assigning|reconciling|stable|dead}

• Streams group rebalances sensor

kafka.server:type=group-coordinator-metrics,name=streams-group-rebalance-rate

kafka.server:type=group-coordinator-metrics,name=streams-group-rebalance-count

Broker Configurations

The new group protocol would be guarded by enabling a new version of the group.version feature flag on the broker side.

Updated properties

New properties

Streams API

In a future major version, when the classic group protocol will be deprecated, the interfaces introduced in KIP-924 would be deprecated, unless an integration with this KIP is proposed in a follow-up KIP.

Streams Configurations

New configurations

Deprecations

In a future major version, when the classic group protocol will be deprecated, the following configuration options will be deprecated:

acceptable.recovery.lag

max.warmup.replicas

num.standby.replicas

probing.rebalance.interval.ms

rack.aware.assignment.strategy

rack.aware.assignment.traffic_cost

rack.aware.assignment.non_overlap_cost

task.assignor.class

Note that both the rack-aware task assignor and customizable client-side task assignment may be introduced into the new protocol in follow-up KIPs (see Future Work section). In this case, the latter 5 configuration options would not be deprecated in the future major version.

Admin API

Add the following methods to the org.apache.kafka.client.admin.AdminClient  interface, mostly backed by the same implementations as the consumer group API.

...

Method signature

...

Description

...

RPC used

...

Group Configurations

We will add new configurations for the resource type GROUP in DescribeConfigs and IncrementalAlterConfigs to override the default broker configurations dynamically for specific groups.

Streams API

In a future major version, when the classic group protocol will be deprecated, the interfaces introduced in KIP-924 would be deprecated, unless an integration with this KIP is proposed in a follow-up KIP.

Streams Configurations

New configurations

Deprecations

In a future major version, when the classic group protocol will be deprecated, the following configuration options will be deprecated:

acceptable.recovery.lag

max.warmup.replicas

num.standby.replicas

probing.rebalance.interval.ms

rack.aware.assignment.tags

rack.aware.assignment.strategy

rack.aware.assignment.traffic_cost

rack.aware.assignment.non_overlap_cost

task.assignor.class

Note that both the rack-aware task assignor and customizable client-side task assignment may be introduced into the new protocol in follow-up KIPs (see Future Work section). In this case, the latter 5 configuration options would not be deprecated in the future major version.

Admin API

Add the following methods to the org.apache.kafka.client.admin.AdminClient  interface, mostly backed by the same implementations as the consumer group API.

These correspond to existing APIs for consumer groups and some of the code will be shared. The main reason for duplicating them is the naming, as the current API uses "consumerGroup" in the name, despite the RPCs just using "group". There are some differences:

• The describeStreamsGroups uses the DescribeStreamsGroup RPC and contains other information than consumer groups.
• A streams group has an extra state -  NOT_READY, and no legacy states from the classic protocol.
• removeMembersFromConsumerGroup will not have a corresponding API in this first version, as it is using the LeaveGroup RPC for classic consumer groups, which is not available for KIP-848-style groups.

Admin

These correspond to existing APIs for consumer groups and some of the code will be shared. The main reason for duplicating them is the naming, as the current API uses "consumerGroup" in the name, despite the RPCs just using "group". There are some differences:

• The describeStreamsGroups uses the DescribeStreamsGroup RPC and contains other information than consumer groups.
• A streams group has an extra state -  NOT_READY, and no legacy states from the classic protocol.
• removeMembersFromConsumerGroup will not have a corresponding API in this first version, as it is using the LeaveGroup RPC for classic consumer groups, which is not available for KIP-848-style groups.

Admin

   /**
    * Alters offsets for the specified group. In order to succeed, the group must be empty.
    *
    * <p>This is a convenience method for {@link #alterStreamsGroupOffsets(String, Map, AlterStreamsGroupOffsetsOptions)} with default options.
    * See the overload for more details.
    *
    * @param groupId The group for which to alter offsets.
    * @param offsets A map of offsets by partition.
    * @return The AlterStreamsGroupOffsetsResult.
    */
   default AlterStreamsGroupOffsetsResult alterStreamsGroupOffsets(String groupId, Map<TopicPartition, Long> offsets) {
       return alterStreamsGroupOffsets(groupId, offsets, new AlterStreamsGroupOffsetsOptions());
   }
 
   /**
    * Alters offsets for the specified group. In order to succeed, the group must be empty.
    *
    * <p>This operation is not transactional so it may succeed for some partitions while fail for others.
    *
    * @param groupId The group for which to alter offsets.
    * @param offsets A map of offsets by partition. Partitions not specified in the map are ignored.
    * @param options The options to use when altering the offsets.
    * @return The AlterStreamsGroupOffsetsResult.
    */
   AlterStreamsGroupOffsetsResult alterStreamsGroupOffsets(String groupId, Map<TopicPartition, Long> offsets, AlterStreamsGroupOffsetsOptions options);
 
   /**
    * DeleteAlters offsets for a set of topics in a Streamsthe specified group. In order to succeed, the group withmust thebe default optionsempty.
    *
    * <p>This is a convenience method for {@link #deleteStreamsGroupOffsets#alterStreamsGroupOffsets(String, SetMap, DeleteStreamsGroupOffsetsOptionsAlterStreamsGroupOffsetsOptions)} with default options.
    * See the overload for more details.
    *
    * @param groupId The group for which to deletealter offsets.
    * @param topics The topics offsets A map of offsets by partition.
    * @return The DeleteStreamsGroupOffsetsResultAlterStreamsGroupOffsetsResult.
    */
   default DeleteStreamsGroupOffsetsResultAlterStreamsGroupOffsetsResult deleteStreamsGroupOffsetsalterStreamsGroupOffsets(String groupId, Set<String> topicsMap<TopicPartition, Long> offsets) {
       return deleteStreamsGroupOffsetsalterStreamsGroupOffsets(groupId, topicsoffsets, new DeleteStreamsGroupOffsetsOptionsAlterStreamsGroupOffsetsOptions());
   }
 
   /**
    * Delete offsets for a set of topics in a Streams groupAlters offsets for the specified group. In order to succeed, the group must be empty.
    *
    * <p>This operation is not transactional so it may succeed for some partitions while fail for others.
    *
    * @param groupId The group for which to deletealter offsets.
    * @param topics The topicsoffsets A map of offsets by partition. Partitions not specified in the map are ignored.
    * @param options The options to use when altering deletingthe offsets in a Streams group.
    * @return The DeleteStreamsGroupOffsetsResultAlterStreamsGroupOffsetsResult.
    */
   DeleteStreamsGroupOffsetsResultAlterStreamsGroupOffsetsResult deleteStreamsGroupOffsetsalterStreamsGroupOffsets(String groupId,
 Map<TopicPartition,      Set<String> topics,
       DeleteStreamsGroupOffsetsOptions Long> offsets, AlterStreamsGroupOffsetsOptions options);
 
   /**
    * Delete Streams groups from the clusteroffsets for a set of topics in a Streams group with the default options.
    *
    * <p>This is a convenience method for {@link #deleteStreamsGroups(Collection<String>#deleteStreamsGroupOffsets(String, Set, DeleteStreamsGroupsOptionsDeleteStreamsGroupOffsetsOptions)} with default options.
    * See the overload for more details.
    *
    * @param groupIdsgroupId The IDsgroup offor the groupswhich to delete offsets.
    * @param topics The topics.
    * @return The DeleteStreamsGroupsResultDeleteStreamsGroupOffsetsResult.
    */
   default DeleteStreamsGroupsResultDeleteStreamsGroupOffsetsResult deleteStreamsGroups(Collection<String> groupIdsdeleteStreamsGroupOffsets(String groupId, Set<String> topics) {
       return deleteStreamsGroups(groupIdsdeleteStreamsGroupOffsets(groupId, topics, new DeleteStreamsGroupsOptionsDeleteStreamsGroupOffsetsOptions());
   }
 
   /**
   }
 
   /**
    * Delete offsets for a set of topics in a Streams group.
    *
    * Delete@param StreamsgroupId groupsThe fromgroup thefor cluster.
which to delete  *offsets.
    * @param groupIdstopics The IDs of the groups to deletetopics.
    * @param options The options to use when deleting offsets in a Streams group.
    * @return The DeleteStreamsGroupsResultDeleteStreamsGroupOffsetsResult.
    */
   DeleteStreamsGroupsResultDeleteStreamsGroupOffsetsResult deleteStreamsGroups(Collection<String> groupIds, DeleteStreamsGroupsOptionsdeleteStreamsGroupOffsets(String groupId,
       Set<String> topics,
       DeleteStreamsGroupOffsetsOptions options);
 
   /**
    * DescribeDelete some Streams groups infrom the cluster, with the default options.
    *
    * <p>This is a convenience method for {@link #describeStreamsGroups#deleteStreamsGroups(CollectionCollection<String>, DescribeStreamsGroupsOptionsDeleteStreamsGroupsOptions)}
 with default options.
 * with default options.* See the overload for more details.
    *
    * @param groupIds The IDs of the groups to describedelete.
    * @return The DescribeStreamsGroupsResultDeleteStreamsGroupsResult.
    */
   default DescribeStreamsGroupsResultDeleteStreamsGroupsResult describeStreamsGroupsdeleteStreamsGroups(Collection<String> groupIds) {
       return describeStreamsGroupsdeleteStreamsGroups(groupIds, new DescribeStreamsGroupsOptionsDeleteStreamsGroupsOptions());
   }
 
   /**
    * Describe someDelete Streams groups infrom the cluster.
    *
    * @param groupIds The IDs of the groups to describedelete.
    * @param options  The options to use when deleting describinga theStreams groupsgroup.
    * @return The DescribeStreamsGroupsResultDeleteStreamsGroupsResult.
    */
   DescribeStreamsGroupsResultDeleteStreamsGroupsResult describeStreamsGroupsdeleteStreamsGroups(Collection<String> groupIds,
                                                     DescribeStreamsGroupsOptions  DeleteStreamsGroupsOptions options);
 
   /**
    * List the Streams group offsets available in* theDescribe clustersome forStreams thegroups specifiedin Streamsthe groupscluster, with the default options.
    *
    * <p>This is a convenience method for {@link #listStreamsGroupOffsets#describeStreamsGroups(MapCollection, ListStreamsGroupOffsetsOptionsDescribeStreamsGroupsOptions)}
    * towith listdefault offsetsoptions. ofSee allthe partitionsoverload for the specified Streams groups with default optionsmore details.
    *
    * @param groupSpecsgroupIds Map of Streams group ids to a spec that specifies the topic partitions The IDs of the groupgroups to list offsets fordescribe.
    * @return The ListStreamsGroupOffsetsResultDescribeStreamsGroupsResult.
    */
   default ListStreamsGroupOffsetsResultDescribeStreamsGroupsResult listStreamsGroupOffsetsdescribeStreamsGroups(Map<String, ListStreamsGroupOffsetsSpec> groupSpecsCollection<String> groupIds) {
       return listStreamsGroupOffsetsdescribeStreamsGroups(groupSpecsgroupIds, new ListStreamsGroupOffsetsOptionsDescribeStreamsGroupsOptions());
   }
 
   /**
    * ListDescribe thesome Streams group offsets availablegroups in the cluster for the specified Streams.
    *
    * @param groupIds The IDs of the groups to describe.
    * @param options  The options to use when describing the groups.
    * @return The DescribeStreamsGroupsResult.
    */
 @param groupSpecs Map of Streams group ids to a spec that specifies the topic partitions of the group to list offsets for.
  DescribeStreamsGroupsResult describeStreamsGroups(Collection<String> groupIds,
                       * @param options The options to use when listing the Streams group offsets.
    * @return The ListStreamsGroupOffsetsResult
    */
   ListStreamsGroupOffsetsResult listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec> groupSpecs, ListStreamsGroupOffsetsOptionsDescribeStreamsGroupsOptions options);
 
   /**
    * List the Streams group groupsoffsets available in the cluster for the specified Streams groups with the default options.
    *
    * <p>This is a convenience method for {@link #listStreamsGroups(ListStreamsGroupsOptions#listStreamsGroupOffsets(Map, ListStreamsGroupOffsetsOptions)}
    * to list offsets of all partitions for the specified Streams groups with default options.
    *
    * See the overload for more details.
    * @param groupSpecs Map of Streams group ids to a spec that specifies the topic partitions of the group to list offsets for.
    * @return The ListStreamsGroupsResult.ListStreamsGroupOffsetsResult
    */
   default ListStreamsGroupsResultListStreamsGroupOffsetsResult listStreamsGroups(listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec> groupSpecs) {
       return listStreamsGroupslistStreamsGroupOffsets(groupSpecs, new ListStreamsGroupsOptionsListStreamsGroupOffsetsOptions());
   }
 
   /**
    * List the Streams group offsets available in the cluster for the specified Streams }groups.
 
   /**
    * List the@param groupSpecs Map of Streams groups available in group ids to a spec that specifies the topic partitions of the cluster.
group to list offsets *for.
    * @param options The options to use when listing the Streams group groupsoffsets.
    * @return The ListStreamsGroupsResult.ListStreamsGroupOffsetsResult
    */
   ListStreamsGroupsResultListStreamsGroupOffsetsResult listStreamsGroups(ListStreamsGroupsOptionslistStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec> groupSpecs, ListStreamsGroupOffsetsOptions options);

AlterStreamsGroupOffsetResult

...

/**
 * A detailed description of a single streams group in the cluster.
 */
public class StreamsGroupDescription {

    public StreamsGroupDescription(
        final String groupId,
        final int groupEpoch,
        final int targetAssignmentEpoch,
        final int topologyEpoch,
        final Collection<StreamsGroupSubtopologyDescription> subtopologies,
        final Collection<StreamsGroupMemberDescription> members,
        final GroupState groupState,
        final StreamsGroupStateNode state,coordinator,
        final Set<AclOperation> authorizedOperations
    );

    /**
     * The id of the streams group.
     */
    public String groupId();
    
    /**
     * The epoch of finalthe Nodeconsumer coordinator,group.
     */
    finalpublic Set<AclOperation>int authorizedOperationsgroupEpoch();
 
    /**
     * The idepoch of the streamstarget groupassignment.
     */
    public Stringint groupIdtargetAssignmentEpoch();
    
      /**
     * The epoch of the currently used topology, or null if uninitialized.
     */
    public Stringint topologyEpoch();
    
    /**
     * A list of the members of the streams group.
     */
    public Collection<StreamsGroupMemberDescription> members();

    /**
     * A list of the subtopologies in the streams group.
     */
    public Collection<StreamsGroupSubtopologyDescription> subtopologies();

    /**
     * The state of the streams group state, or UNKNOWN if the state is too new for us to parse.
     */
    public StreamsGroupStateGroupState stategroupState();

    /**
     * The streams group coordinator, or null if the coordinator is not known.
     */
    public Node coordinator();

    /**
     * authorizedOperations for this group, or null if that information is not known.
     */
    public Set<AclOperation> authorizedOperations();
}

...

/**
 * A detailed description of a single member in the group.
 */
public class StreamsGroupMemberDescription {

    public StreamsGroupMemberDescription(
        final String memberId, 
        final Optional<String>int instanceIdmemberEpoch,
        final Stringint clientIdcurrentAssignmentEpoch,
        final StringOptional<String> clientHostinstanceId,
        final intOptional<String> topologyEpochrackId,
        final String processIdclientId,
        final Map<String, String> clientTagsString clientHost,
        final List<TaskOffset>int taskOffsetstopologyEpoch, 
        final List<TaskOffset>String taskEndOffsetsprocessId,
        final StreamsGroupMemberAssignmentOptional<Endpoint> assignmentuserEndpoint,
        final Optional<StreamsGroupMemberAssignment> targetAssignment);

    /**Map<String, String> clientTags,
     * The id offinal the group member.List<TaskOffset> taskOffsets,
     */
   final public String memberId();

    /**
     * The id of the instance, used for static membership, if available.List<TaskOffset> taskEndOffsets,
     */
    public Optional<String> instanceId();

    /**final StreamsGroupMemberAssignment assignment,
     * The client idfinal ofStreamsGroupMemberAssignment thetargetAssignment,
 group member.
     */
 final boolean isClassic
 public String clientId( );

    /**
     * The hostid of the group member.
     */
    public String clientHostmemberId();

    /**
     * The epoch of the topology present on the clientgroup member.
     */
    public int topologyEpochmemberEpoch();

  
    /**
     * IdentityThe id of the streamsinstance, instanceused thatfor maystatic havemembership, multipleif clientsavailable.
     */
    public StringOptional<String> processIdinstanceId(); 
    
    /**
     * Used for rack-aware assignment algorithmThe rack ID of the group member.
     */
    public Map<String, String> clientTagsOptional<String> rackId();
    
    /**
     * Cumulative offsets for tasks The client id of the group member.
     */
    public List<TaskOffset>String taskOffsetsclientId();

    /**
     * CumulativeThe taskhost changelogof endthe offsetsgroup for tasksmember.
     */
    public List<TaskOffset>String taskEndOffsetsclientHost();

    /**
     * The current assignment. epoch of the group member. 
     */
    public StreamsGroupMemberAssignmentint assignmentmemberEpoch();

    /**
     * The target epoch of the current assignment.
     */
    public Optional<StreamsGroupMemberAssignment>int targetAssignmentcurrentAssignmentEpoch();
    
    /**
     * The cumulative offset for one task.
      /**/
    public static* classThe TaskOffsetepoch {

of the topology present on the client.
  public TaskOffset(final String subtopology,*/
 final int partition, finalpublic longint offsettopologyEpoch();
 
           /**
     * Identity of the *streams Theinstance subtopologythat identifier.
may have multiple clients.
      */
        public String subtopologyprocessId(); 

        /**
         * TheUser-defined partitionendpoint offor theInteractive taskQueries.
         */
        public intOptional<Endpoint> partitionuserEndpoint();

         /**
         * TheUsed cumulativefor offset (sum of offsets in all input partitions).
    rack-aware assignment algorithm.
     */
    public Map<String,   public long offsetString> clientTags();

    }
}

StreamsGroupMemberAssignment

/**
 * A description of the* assignmentsCumulative of a specific streams group memberoffsets for tasks.
  */
public class StreamsGroupMemberAssignment {*/

    public List<TaskOffset> StreamsGroupMemberAssignmenttaskOffsets();

    /**
     final* List<TaskIds>Cumulative activeTasks,
task changelog end offsets for tasks.
   final List<TaskIds> standbyTasks,*/
    public    final List<TaskIds> warmupTasksList<TaskOffset> taskEndOffsets();

    /**
     * ActiveThe tasks for this clientcurrent assignment.
     */
    public List<TaskIds>StreamsGroupMemberAssignment activeTasksassignment();

    /**
     * StandbyThe tasks for this clienttarget assignment.
     */
    public List<TaskIds>StreamsGroupMemberAssignment standbyTaskstargetAssignment();     
    
    /**
     * Warmup tasks for this clientThe flag indicating whether a member is classic.
     */
    public List<TaskIds>boolean warmupTasksisClassic();

     /**
     * The Allcumulative tasksoffset for one subtopology of a membertask.
     */
    public static class TaskIds {
TaskOffset {

        public TaskOffset(final String subtopologyId, final int partition, final long offset);

        /**
         * The subtopology identifier.
         */
        public TaskIds(final String subtopology, final List<Integer> partitionssubtopologyId();

        /**
         * The subtopology identifierpartition of the task.
         */
        public Stringint subtopologypartition();

        /**
         * The partitionscumulative ofoffset the(sum inputof topicsoffsets processedin byall thisinput memberpartitions).
         */
        public List<Integer>long partitionsoffset();
    }
}

...

StreamsGroupMemberAssignment

/**
 * A detailed descriptiondescription of the assignments of a specific streams singlegroup subtopologymember.
 */
public class StreamsGroupSubtopologyDescriptionStreamsGroupMemberAssignment {

    public StreamsGroupSubtopologyDescriptionStreamsGroupMemberAssignment(
        final String subtopology,
        final List<String> sourceTopics,
        final List<String> repartitionSinkTopics,
        final Map<String, TopicInfo> stateChangelogTopics,
        final Map<String, TopicInfo> repartitionSourceTopics);

    /**
     * String to uniquely identify the subtopology.
     */
    public String subtopology();

    /**
List<TaskIds> activeTasks,
       * Thefinal topicsList<TaskIds> thestandbyTasks,
 topology reads from.
     */
final List<TaskIds> warmupTasks
  public List<String> sourceTopics();

    /**
     * TheActive repartitiontasks topicsfor the topology writes tothis client.
     */
    public List<String>List<TaskIds> repartitionSinkTopicsactiveTasks();

    /**
     * TheStandby settasks of state changelog topics associated with this sub-topologyfor this client.
     */
    public Map<String, TopicInfo> stateChangelogTopicsList<TaskIds> standbyTasks();
    
    /**
     * TheWarmup settasks offor source topics that are internally created repartition topicsthis client.
     */
    public Map<String, TopicInfo> repartitionSourceTopicsList<TaskIds> warmupTasks();

    /**
     * Information aboutAll tasks for one subtopology of a topicmember.
     */
    public static class TopicInfoTaskIds {

        public TopicInfoTaskIds(final intString partitionssubtopologyId, final Map<String, String> topicConfigsList<Integer> partitions);

        /**
         * The number of partitions in the topicsubtopology identifier.
         */
        public intString partitionssubtopologyId();

        /**
         * The Configurationspartitions of the topic input topics processed by this member.
         */
        public Map<String, String> topicConfigsList<Integer> partitions();
    }

}

...

StreamsGroupSubtopologyDescription

package org.apache.kafka.client.admin;
  
/**
 * Options for {@link Admin#describeStreamsGroups(Collection<String>, DescribeStreamsGroupsOptions)}.
 *
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class DescribeStreamsGroupsOptions extends AbstractOptions<DescribeStreamsGroupsOptions> {
    public DescribeStreamsGroupsOptions includeAuthorizedOperations(boolean includeAuthorizedOperations);
 
    public boolean includeAuthorizedOperations();
}

ListStreamsGroupOffsetsResult

package org.apache.kafka.clients.admin;
  
/**
 * The result of the {@link Admin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)} call.
 * <p>
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupOffsetsResult {/**
 * A detailed description of a single subtopology
 */
public class StreamsGroupSubtopologyDescription {

    public StreamsGroupSubtopologyDescription(
        final String subtopologyId,
        final List<String> sourceTopics,
        final List<String> repartitionSinkTopics,
        final Map<String, TopicInfo> stateChangelogTopics,
        final Map<String, TopicInfo> repartitionSourceTopics);

    /**
     * String to uniquely identify the subtopology.
     */
    public String subtopologyId();

    /**
     * ReturnThe atopics futurethe whichtopology yieldsreads allfrom.
 Map<String, Map<TopicPartition, Long> objects, if*/
 requests for all thepublic groups succeed.List<String> sourceTopics();

     /**/
     * The publicrepartition KafkaFuture<Map<String,topics Map<TopicPartition,the Long>>>topology all() {writes to.
    } */
    public List<String> repartitionSinkTopics();

    /**
     * Return a future which yields a mapThe set of topicstate partitionschangelog totopics offsetsassociated forwith thethis specified groupsubtopology.
     */
    public KafkaFuture<Map<TopicPartitionMap<String, Long>>TopicInfo> partitionsToOffset(String groupId) {
    }
}

ListStreamsGroupOffsetsOptions

package org.apache.kafka.client.admin;
  
/**
 * Options for {@link Admin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)}.
 * <p>
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupOffsetsOptions extends AbstractOptions<ListStreamsGroupOffsetsOptions> {
}

ListStreamsGroupOffsetsSpec

package org.apache.kafka.client.admin;
  
/**
 * Specification of Streams group offsets to list using {@link Admin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)}.
 * <p>
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupOffsetsSpec {
  public ListStreamsGroupOffsetsSpec();
 
  /**
   * Set the topic partitions whose offsets are to be listed for a Streams group.
   */
  ListStreamsGroupOffsetsSpec topicPartitions(Collection<TopicPartition> topicPartitions);
 
  /**
   * Returns the topic partitions whose offsets are to be listed for a Streams group.
   */
  Collection<TopicPartition> topicPartitions();
}

...

stateChangelogTopics();

    /**
     * The set of source topics that are internally created repartition topics.
     */
    public Map<String, TopicInfo> repartitionSourceTopics();

    /**
     * Information about a topic.
     */
    public static class TopicInfo {

        public TopicInfo(final int partitions, final Map<String, String> topicConfigs);

        /**
         * The number of partitions in the topic.
         */
        public int partitions();

        /**
         * Configurations of the topic.
         */
        public Map<String, String> topicConfigs();
    }

}

DescribeStreamsGroupsOptions

package org.apache.kafka.clientsclient.admin;
  
/**
 * TheOptions result offor the {@link Admin#listStreamsGroups(ListStreamsGroupsOptionsAdmin#describeStreamsGroups(Collection<String>, DescribeStreamsGroupsOptions)} call.
 * <p>
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupsResultDescribeStreamsGroupsOptions {
extends AbstractOptions<DescribeStreamsGroupsOptions>   /**{
    public *DescribeStreamsGroupsOptions Returns a future that yields either an exception, or the full set of Streams group listings.
     */includeAuthorizedOperations(boolean includeAuthorizedOperations);
 
    public KafkaFuture<Collection<StreamsGroupListing>>boolean allincludeAuthorizedOperations();
}

ListStreamsGroupOffsetsResult

package org.apache.kafka.clients.admin;
  
 {
    }
 
    /**
     * ReturnsThe aresult futureof whichthe yields just the valid listings{@link Admin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)} call.
 * <p>
 * The */
API of this class publicis KafkaFuture<Collection<StreamsGroupListing>> valid()evolving, see {
@link Admin} for  }
  details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupOffsetsResult {
    /**
     * ReturnsReturn a future which yields just all Map<String, Map<TopicPartition, Long> objects, if requests for all the errorsgroups which occurredsucceed.
     */
    public KafkaFuture<Collection<Throwable>> errors KafkaFuture<Map<String, Map<TopicPartition, Long>>> all() {
    }
}

StreamsGroupListing

package org.apache.kafka.client.admin;
 
import org.apache.kafka.common.StreamsGroupState;
 

    /**
 * A listing of a* StreamsReturn groupa infuture thewhich cluster.
yields *a <p>
map *of Thetopic APIpartitions ofto thisoffsets classfor isthe evolving, see {@link Admin} for details.
specified group.
     */
@InterfaceStability.Evolving
public  class StreamsGroupListing {
public KafkaFuture<Map<TopicPartition, publicLong>> StreamsGroupListingpartitionsToOffset(String groupId); {
  public StreamsGroupListing(String groupId, Optional<StreamsGroupState> state);
 
   }
}

ListStreamsGroupOffsetsOptions

package org.apache.kafka.client.admin;
  
/**
   * TheOptions idfor of the Streams group{@link Admin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)}.
 * <p>
 */
 The publicAPI String groupId();
 
  /**
   * The Streams group state.
   */
  public Optional<StreamsGroupState> state();
}

...

of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupOffsetsOptions extends AbstractOptions<ListStreamsGroupOffsetsOptions> {
}

ListStreamsGroupOffsetsSpec

package org.apache.kafka.client.admin;
 
import org.apache.kafka.common.StreamsGroupState;
 
/**
 * Options for Specification of Streams group offsets to list using {@link Admin#listStreamsGroups(ListStreamsGroupsOptionsAdmin#listStreamsGroupOffsets(Map<String, ListStreamsGroupOffsetsSpec>, ListStreamsGroupOffsetsOptions)}.
 * <p>
 * The API of this class is evolving, see {@link Admin} for details.
 */
@InterfaceStability.Evolving
public class ListStreamsGroupsOptionsListStreamsGroupOffsetsSpec {
 extends AbstractOptions<ListStreamsGroupsOptions> {public ListStreamsGroupOffsetsSpec();
 
   /**
     * IfSet statesthe istopic set, only groups in these states willpartitions whose offsets are to be returned.listed Otherwise,for alla groupsStreams are returnedgroup.
     */
    public ListStreamsGroupsOptions inStates(Set<StreamsGroupState> statesListStreamsGroupOffsetsSpec topicPartitions(Collection<TopicPartition> topicPartitions);
 
    /**
     * ReturnReturns the listtopic ofpartitions Stateswhose thatoffsets are requestedto orbe emptylisted iffor noa states have been specifiedStreams group.
     */
    public Set<StreamsGroupState> statesCollection<TopicPartition> topicPartitions();
}

GroupType

Another case is added to the org.apache.kafka.common.GroupType  enum:

StreamsGroupState

GroupState

Another case is added to theA new enum org.apache.kafka.common.StreamsGroupStateGroupState  is addedenum:

NOT_READY

Exceptions

The following new exception is exceptions are added to the org.apache.kafka.common.errors package, corresponding to the new error codes in the Kafka protocol.

• StreamsInvalidTopology  - The supplied topology is invalid. Returned if the client sends a topology that does not fulfill the expected invariants.

StreamsInvalidTopology is fatal.

Command-line tools

.

• StreamsInvalidTopologyException  - The supplied topology is invalid. Returned if the client sends a topology that does not fulfill the expected invariants.
• StreamsInvalidTopologyEpochException  - The client provided a invalid topology epoch with respect to the stream group state, for example, the topology was changed by the epoch not bumped.
• StreamsTopologyFencedException  - When a client attempts to join with an outdated topology epoch.

Command-line tools

kafka-groups.sh

We add an option --streams  to the above commad-line tool, which filter the groups to show share groups. Furthermore streams  becomes one of the possible values for --group-type . 

kafka-streams-groups.sh

A new tool called kafka-streams-groups.sh is added for working with streams groups. It has the following options:

...

• KIP-848 originally envisioned that Kafka Streams continues to using a byte-array metadata protocol on top of regular consumer group RPCs, and use a client-side assignor, and provided a rough proposal how to do so. The described approach was never implemented. In this KIP, we propose to use broker-side assignment by default for several reasons (mostly already mentioned in the motivation section):

  • Client-side assignment makes it hard to debug and tune the assignment logic, where a simple parameter change requires redeploying of all streams clients.

  • Using opaque byte-arrays to exchange the required metadata makes it hard to understand the state of a streams group on the protocol level. One has to discover the information from logs spread across all client machines. Central mechanisms of the Kafka protocol, such as versioning of RPCs, needs to be reimplemented on the level of RPCs.

  • One could argue that the Kafka protocol is simpler without Kafka Streams specific RPCs, but we think the opposite is true. The KIP-848 consumer group protocol was extended with client-side assignment, byte-array metadata and metadata versioning just for Kafka Streams. Having the concerns of Kafka Streams dealt with in separate RPCs mainly introduces a clearer separation and gives the Kafka community the ability to simplify the upcoming consumer protocol.

• Instead of using a separate initialize RPCthe heartbeat RPC during joining to initialize the topology, we considered just using the heartbeat with memberEpoch=0 to initialize the Streams group and initiate the creation of all topics. This would have a number of downsides, such as that every member needs to send the initialization data every time they start (and the initialization data may be large already in the current schema and may grow larger in the future), and the heartbeat requiring the ACL for creating topics. Furthermore, since the initialization may take a certain amount of time, we’d likely still have to respond to the initial heartbeat without having fully initialized the group, leading to temporary “initializing” state for the group that we also get in this proposala dedicated group intialization RPC. Using the heartbeat RPC for initialization turned out to be simpler and we realized that the drawbacks that we wanted to avoid with the dedicated initialization RPC where not that significant. For example, we thought that we could save on data sent for intitialization with a dedicated intialization call. However, sending the topology metadata in the heartbeat when joining does not seem to be too much and we can ensure all clients use the same topology metadata. Also with two different calls we had the overhead to coordinate the initialization and the heartbeat requests.

• An earlier draft of this KIP proposed introducing optional client-side task assignment, that would allow customization of the task assignment similar to KIP-924. We decided to remove it from this KIP, to limit the scope of the KIP and not introduce features in the protocol whose use we cannot fully envision yet. The RPCs defined in this KIP are, however, defined in a way that they could easily be extended with client-side assignment in a follow-up KIP, possibly together with a public interface for adding custom task assignors on the client side.

...