THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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| Consumer Group | ||
|---|---|---|
| Name | Type | Description |
| Group ID | string | The group ID as configured by the consumer. The ID uniquely identifies the group. |
| Group Epoch | int32 | The current epoch of the group. The epoch is incremented by the group coordinator when a new assignment is required for the group. |
| Members | []Member | The set of members in the group. |
| Partitions Metadata | []PartitionMetadata | The metadata of the partitions that the group is subscribed to. This is used to detect partition metadata changes. |
| Member | ||
| Name | Type | Description |
| Member ID | string | The unique identifier of the member. It is generated by the client upon startup coordinator upon the first heartbeat request and must be used during the lifetime of the member. The ID is similar to an incarnation ID. |
| Instance ID | string | The instance ID configured by the consumer. |
| Rack ID | string | The rack ID configured by the consumer. |
| Client ID | string | The client ID configured by the consumer. |
| Client Host | string | The client host configured by the consumer. |
| Subscribed Topic Names | []string | The current set of subscribed topic names configured by the consumer. |
| Subscribed Topic Regex | string | The current subscription regular expression configured by the consumer. |
| Server Assignor | string | The server side assignor used by the group. |
| Client Assignors | []Assignor | The list of client-side assignors supported by the member. The order of this list defined the priority. |
| Assignor | ||
| Name | Type | Description |
| Name | string | The unique name of the assignor. |
| Reason | int8 | The reason why the metadata was updated. |
| Minimum Version | int16 | The minimum version of the metadata schema supported by this assignor. |
| Maximum Version | int16 | The maximum version of the metadata schema supported by this assignor. |
| Version | int16 | The version used to encode the metadata. |
| Metadata | bytes | The metadata provided by the consumer for this assignor. |
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Every member is uniquely identified by a UUID. This is is called the Member ID. This UUID is generated on the client sideserver side and given to the member when it joins the group. It is used in all the communication with the group coordinator and must be kept during the entirely life span of the member (e.g. the consumer). In that sense, it is similar to an incarnation ID.
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| Code Block | ||
|---|---|---|
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{
"apiKey": TBD,
"type": "request",
"listeners": ["zkBroker", "broker"],
"name": "ConsumerGroupHeartbeatRequest",
"validVersions": "0",
"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 clientcoordinator. The member id must be kept during the entire lifetime of the member." },
{ "name": "MemberEpoch", "type": "int32", "versions": "0+",
"about": "The current member epoch; 0 to join the group; -1 to leave the group." },
{ "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 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 consumer otherwise." },
{ "name": "RebalanceTimeoutMs", "type": "int32", "versions": "0+", "default": -1,
"about": "-1 if it didn't chance since the last heartbeat; the maximum time in milliseconds that the coordinator will wait on the member to revoke its partitions otherwise." },
{ "name": "SubscribedTopicNames", "type": "[]string", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if it didn't change since the last heartbeat; the subscribed topic names otherwise." },
{ "name": "SubscribedTopicRegex", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if it didn't change since the last heartbeat; the subscribed topic regex otherwise" },
{ "name": "ServerAssignor", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if not used or if it didn't change since the last heartbeat; the server side assignor to use otherwise." },
{ "name": "ClientAssignors", "type": "[]Assignor", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if not used or if it didn't change since the last heartbeat; the list of client-side assignors otherwise.", "fields": [
{ "name": "Name", "type": "string", "versions": "0+",
"about": "The name of the assignor." },
{ "name": "MinimumVersion", "type": "int16", "versions": "0+",
"about": "The minimum supported version for the metadata." },
{ "name": "MaximumVersion", "type": "int16", "versions": "0+",
"about": "The maximum supported version for the metadata." },
{ "name": "Reason", "type": "int8", "versions": "0+",
"about": "The reason of the metadata update." },
{ "name": "MetadataVersion", "type": "int16", "versions": "0+",
"about": "The version of the metadata." },
{ "name": "MetadataBytes", "type": "bytes", "versions": "0+",
"about": "The metadata." }
]},
{ "name": "TopicPartitions", "type": "[]TopicPartitions", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if it didn't change since the last heartbeat; the partitions owned by the member.", "fields": [
{ "name": "TopicId", "type": "uuid", "versions": "0+",
"about": "The topic ID." },
{ "name": "Partitions", "type": "[]int32", "versions": "0+",
"about": "The partitions." }
]}
]
} |
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| Code Block | ||||
|---|---|---|---|---|
| ||||
{
"apiKey": TBD,
"type": "response",
"name": "ConsumerGroupHeartbeatResponse",
"validVersions": "0",
"flexibleVersions": "0+",
// Supported errors:
// - GROUP_AUTHORIZATION_FAILED
// - NOT_COORDINATOR
// - COORDINATOR_NOT_AVAILABLE
// - COORDINATOR_LOAD_IN_PROGRESS
// - INVALID_REQUEST
// - UNKNOWN_MEMBER_ID
// - FENCED_MEMBER_EPOCH
// - UNSUPPORTED_ASSIGNOR
// - UNRELEASED_INSTANCE_ID
"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": "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 generated by the coordinator. Only provided when the member joins with MemberEpoch == 0." },
{ "name": "MemberEpoch", "type": "int32", "versions": "0+",
"about": "The member epoch." },
{ "name": "ShouldComputeAssignment", "type": "bool", "versions": "0+",
"about": "True if the member should compute the assignment for the group." },
{ "name": "HeartbeatIntervalMs", "type": "int32", "versions": "0+",
"about": "The heartbeat interval in milliseconds." },
{ "name": "Assignment", "type": "Assignment", "versions": "0+", "nullableVersions": "0+", "default": "null",
"about": "null if not provided; the assignment otherwise.", "fields": [
{ "name": "Error", "type": "int8", "versions": "0+",
"about": "The assigned error." },
{ "name": "AssignedTopicPartitions", "type": "[]TopicPartitions", "versions": "0+",
"about": "The partitions assigned to the member that can be used immediately." },
{ "name": "PendingTopicPartitions", "type": "[]TopicPartitions", "versions": "0+",
"about": "The partitions assigned to the member that cannot be used because they are not released by their former owners yet." },
{ "name": "MetadataVersion", "type": "int16", "versions": "0+",
"about": "The version of the metadata." },
{ "name": "MetadataBytes", "type": "bytes", "versions": "0+",
"about": "The assigned metadata." }
]}
],
"commonStructs": [
{ "name": "TopicPartitions", "versions": "0+", "fields": [
{ "name": "TopicId", "type": "uuid", "versions": "0+",
"about": "The topic ID." },
{ "name": "Partitions", "type": "[]int32", "versions": "0+",
"about": "The partitions." }
]}
]
} |
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We considered storing the dynamic group configurations in the group coordinator in order to have the ability to tight their lifecycles to their group. We discarded this approach for two reasons: 1) This pattern does not fit very well in the IncrementalAlterConfig API as it would require to send updates about groups to the coordinator whereas all the other updates go to the controller; and 2) It seems preferable to decouple the life cycle of the dynamic configurations from the life cycle of the groups. Users may want to create configurations before the group is created and users may want to keep their configurations if the group is recreated.
Client side generated Member ID
We considered letting the client generate its member ID (or UUID) instead of relying on the coordinator to generate one when the member joins the group. We ultimately rejected this because 1) it introduces extra dependencies on the client. For instance in C++, UUID are not natively supported so an extra library must be used; and 2) the client could not generate it correctly.
Future Work
Eventually, we aim at deprecating the current membership/rebalance API. In order to get to this point, we would need to first move all the use cases away from it.
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