Status

Current state: Under Discussion Accepted

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: KAFKA-6576

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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• Name: client.quota.callback.class
• Type: CLASS
• Mode: Dynamically configurable as cluster-default for all brokers in the cluster
• Description: The fully qualified name of a class that implements the ClientQuotaCallback interface, which is used to determine quota limits applied to client requests. By default, <user, client-id>, <user> or <client-id> quotas stored in ZooKeeper are applied. For any given request, the most specific quota that matches the user principal of the session and the client-id of the request is enforced by every broker.

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The following new public classes/traits will be introduced in the package org.apache.kafka.server.quota (in the Kafka core clients project).

The quota types supported for the callback will be FetchFETCH/ProducePRODUCE/RequestREQUEST.

objectpublic enum ClientQuotaType  {
    casePRODUCE,
 object Fetch extends ClientQuotaTypeFETCH,
  case object Produce extends ClientQuotaType
  case object Request extends ClientQuotaType
}
sealed trait ClientQuotaTypeREQUEST
}

 ClientQuotaCallback must be implemented by custom callbacks. It will also be implemented by the default quota callback.  Callback implementations should cache persisted configs if necessary to determine quotas quickly since ClientQuotaCallback.quota() will be invoked on every request.

trait ClientQuotaCallback extends Configurable {

  /**
    * Quota callback invokedinterface tofor determinebrokers thethat quotaenables limitcustomization toof beclient applied for a requestquota computation.
 */
public interface ClientQuotaCallback *extends Configurable {

    /**
 @param session The session for* whichQuota quotacallback isinvoked requested
to determine the quota *metric @paramtags clientIdto Thebe clientapplied idfor associated with the request
a request.
     * Quota @paramlimits quotaTypeare Typeassociated ofwith quota requested
metrics and all clients *which use the same
     * metric tags share the quota limit.
     *
     * @param quotaType @returnType theof quota includingrequested
 the limit and metric tags* that@param principal indicateThe whichuser otherprincipal entitiesof sharethe thisconnection quota
for which quota is */requested
  def quota(session: Session, clientId:* String,@param quotaType:clientId ClientQuotaType): ClientQuota

  /**
    * Metadata update callback that is invoked whenever UpdateMetadata request is received from
 The client id associated with the request
     * the@return controller.quota Thismetric istags usefulthat ifindicate quotawhich computationother isclients takesshare partitionsthis intoquota
 account.
    * /
    *Map<String, @paramString> partitions Partitions and their metadata including partition leaderquotaMetricTags(ClientQuotaType quotaType, KafkaPrincipal principal, String clientId);

    /*/*
  def updatePartitionMetadata(partitions: Map[TopicPartition, PartitionMetadata]): Unit

  /**
    * Quota configuration update callback that is invoked whenever quota configuration in ZooKeeper
    * is updated. This is useful to track configured quotas if the built-in quota configuration tools
    * are used.
    * 
    * @param quotaEntity The quota entity for which quota is being updated.
    * @param quotaType Type of quota being updated.
    * @param newValue The new quota value. If None, the quota configuration for `quotaEntity` is deleted.
    */
  def updateQuota(quotaEntity: ClientQuotaEntity, quotaType: ClientQuotaType, newValue: Option[Double]) : Unit

  /**
    * Closes this instance.
    */
  def close(): Unit
}

The quota returned by the callback should include the quota limit as well the metric tags to be used. These tags determine which entities share the quota.

By default the tags "user" and "client-id" will be used for all quota metrics. When <user, client-id> quota config is used, user tag is set to user principal of the session and client-id tag is set to the client-id of the request. If <user> quota config is used, user tag is set to user principal of the session and client-id tag is set to empty string. Similarly, if <client-id> quota config is used, the user tag is set to empty string. This ensures that the same quota sensors and metrics are shared by all requests that match each quota config.

/**
  * Client quota returned by `ClientQuotaCallback`.
  *
  * @param quotaLimit The quota bound to be applied
  * @param metricTags The tags to be added to the quota metric for this request. All entities
  *                   which have the same `metricTags` share the `quotaLimit`
  */
case class ClientQuota(quotaLimit: Double, metricTags: Map[String, String])

When quota configuration is updated in ZooKeeper, quota callbacks are notified of configuration changes. Quota configuration entities can be combined to define quotas at different levels.

object QuotaConfigEntityType  {
  case object User extends QuotaConfigEntityType
  case object ClientId extends QuotaConfigEntityType
  case object DefaultUser extends QuotaConfigEntityType
  case object DefaultClientId extends QuotaConfigEntityType
}
sealed trait QuotaConfigEntityType

trait QuotaConfigEntity {
  def name: String
  def entityType: QuotaConfigEntityType
}

/**
  * The metadata for an entity for which quota is configured. Quotas may be defined at
  * different levels and `configEntities` gives the config entities that define the level.
  * For example, if quota is configured for <userA, clientB>, `configEntities` will be
  * List(userA, clientB). For <clientC> quota, 'configEntities` will be List(clientC).
  */
trait ClientQuotaEntity {
  def configEntities: List[QuotaConfigEntity]
}

When partition leaders change, controller notifies brokers using UpdateMetadata request. Quota callbacks are notified of metadata changes so that callbacks that base quota computation on partitions have access to the current metadata.

/**
  * Partition metadata that may be used in quota computation. This is provided
  * by the broker when UpdateMetadata request is received from the controller.
  */
trait PartitionMetadata {
  def leader: Int
}

 * Returns the quota limit associated with the provided metric tags. These tags were returned from
     * a previous call to {@link #quotaMetricTags(ClientQuotaType, KafkaPrincipal, String)}. This method is
     * invoked by quota managers to obtain the current quota limit applied to a metric when the first request
     * using these tags is processed. It is also invoked after a quota update or cluster metadata change.
     * If the tags are no longer in use after the update, (e.g. this is a {user, client-id} quota metric
     * and the quota now in use is a {user} quota), null is returned.
     *
     * @param quotaType  Type of quota requested
     * @param metricTags Metric tags for a quota metric of type `quotaType`
     * @return the quota limit for the provided metric tags or null if the metric tags are no longer in use
     */
    Double quotaLimit(ClientQuotaType quotaType, Map<String, String> metricTags);

    /**
     * Quota configuration update callback that is invoked when quota configuration for an entity is
     * updated in ZooKeeper. This is useful to track configured quotas if built-in quota configuration
     * tools are used for quota management.
     *
     * @param quotaType   Type of quota being updated
     * @param quotaEntity The quota entity for which quota is being updated
     * @param newValue    The new quota value
     */
    void updateQuota(ClientQuotaType quotaType, ClientQuotaEntity quotaEntity, double newValue);

    /**
     * Quota configuration removal callback that is invoked when quota configuration for an entity is
     * removed in ZooKeeper. This is useful to track configured quotas if built-in quota configuration
     * tools are used for quota management.
     *
     * @param quotaType   Type of quota being updated
     * @param quotaEntity The quota entity for which quota is being updated
     */
    void removeQuota(ClientQuotaType quotaType, ClientQuotaEntity quotaEntity);

    /**
     * Returns true if any of the existing quota configs may have been updated since the last call
     * to this method for the provided quota type. Quota updates as a result of calls to
     * {@link #updateClusterMetadata(Cluster)}, {@link #updateQuota(ClientQuotaType, ClientQuotaEntity, double)}
     * and {@link #removeQuota(ClientQuotaType, ClientQuotaEntity)} are automatically processed.
     * So callbacks that rely only on built-in quota configuration tools always return false. Quota callbacks
     * with external quota configuration or custom reconfigurable quota configs that affect quota limits must
     * return true if existing metric configs may need to be updated. This method is invoked on every request
     * and hence is expected to be handled by callbacks as a simple flag that is updated when quotas change.
     *
     * @param quotaType Type of quota
     */
    boolean quotaResetRequired(ClientQuotaType quotaType);

    /**
     * Metadata update callback that is invoked whenever UpdateMetadata request is received from
     * the controller. This is useful if quota computation takes partitions into account.
     * Topics that are being deleted will not be included in `cluster`.
     *
     * @param cluster Cluster metadata including partitions and their leaders if known
     * @return true if quotas have changed and metric configs may need to be updated
     */
    boolean updateClusterMetadata(Cluster cluster);

    /**
     * Closes this instance.
     */
    void close();
}

The callback is invoked to obtain the quota limit as well the metric tags to be used. These metric tags determine which entities share the quota.

By default the tags "user" and "client-id" will be used for all quota metrics. When <user, client-id> quota config is used, user tag is set to user principal of the session and client-id tag is set to the client-id of the request. If <user> quota config is used, user tag is set to user principal of the session and client-id tag is set to empty string. Similarly, if <client-id> quota config is used, the user tag is set to empty string. This ensures that the same quota sensors and metrics are shared by all requests that match each quota config.

When quota configuration is updated in ZooKeeper, quota callbacks are notified of configuration changes. Quota configuration entities can be combined to define quotas at different levels.

/**
 * The metadata for an entity for which quota is configured. Quotas may be defined at
 * different levels and `configEntities` gives the list of config entities that define
 * the level of this quota entity.
 */
public interface ClientQuotaEntity {
    /**
     * Entity type of a {@link ConfigEntity}
     */
    public enum ConfigEntityType {
        USER,
        CLIENT_ID,
        DEFAULT_USER,
        DEFAULT_CLIENT_ID
    }

    /**
     * Interface representing a quota configuration entity. Quota may be
     * configured at levels that include one or more configuration entities.
     * For example, {user, client-id} quota is represented using two
     * instances of ConfigEntity with entity types USER and CLIENT_ID.
     */
    public interface ConfigEntity {
        /**
         * Returns the name of this entity. For default quotas, an empty string is returned.
         */
        String name();

        /**
         * Returns the type of this entity.
         */
        ConfigEntityType entityType();
    }

    /**
     * Returns the list of configuration entities that this quota entity is comprised of.
     * For {user} or {clientId} quota, this is a single entity and for {user, clientId}
     * quota, this is a list of two entities.
     */
    List<ConfigEntity> configEntities();
}

When partition leaders change, controller notifies brokers using UpdateMetadata request. Quota callbacks are notified of metadata changes so that callbacks that base quota computation on partitions have access to the current metadata. The existing public interface org.apache.kafka.common.Cluster will be used for metadata change notification. 

Proposed Changes

ClientQuotaManager and ClientRequestQuotaManager will be updated to move quota configuration management into a new class DefaultQuotaCallback  that implements ClientQuotaCallback. If a custom callback is not configured, DefaultQuotaCallback will be used.

If a custom callback is configured, it will be instantiated when the broker is started. DynamicBrokerConfig will be updated to handle changes to the callback. KafkaApis will invoke quotaCallback.updatePartitionMetadataupdateClusterMetadata when UpdateMetadata request is received from the controller. This will be ignored by the default quota callback. When ConfigHandler invokes ClientQuotaManager.updateQuota to process dynamic quota config updates, quotaCallback.updateQuota will be invoked. The existing logic to process quota updates will be moved to the default quota callback.

...

We could implement different quota algorithms in Kafka and support quota groups, partition-based quotas etc. But this would require Kafka to manage these groups, mapping of users to partitions etc, increasing the complexity of the code. Since it will be hard to include support for all possible scenarios into the broker code, it will be simpler to make quota computation configurable. This also enables the computation to be altered dynamically without restarting the broker since the new option will be a dynamic broker config.

Enable management of client quotas and replication quotas using a single callback interface


The configuration and management of replication quotas are completely separate from client quota management in the broker. Since the configuration entities are different, it will be simpler to keep them separate. It is not clear if there are scenarios that require custom replication quotas, so this KIP only addresses client quotas.

new option will be a dynamic broker config.

Enable management of client quotas and replication quotas using a single callback interface


The configuration and management of replication quotas are completely separate from client quota management in the broker. Since the configuration entities are different, it will be simpler to keep them separate. It is not clear if there are scenarios that require custom replication quotas, so this KIP only addresses client quotas.

Use Scala traits for public interfaces similar to Authorizer


For compatibility reasons, we are now using Java rather than Scala for all pluggable interfaces including those on the broker. There is already a KIP to move Authorizer to Java as well. As we will be removing support for Java 7 in the next release, we can also use default methods in Java when we need to update pluggable Java interfaces. So the plan is to use Java for all new pluggable interfaces.