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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. They can be configured both globally on the broker, and dynamically for specific streams groups through the IncrementalAlterConfigs and DescribeConfigs RPCs.

Online Migration from a Classic Consumer Group to a Streams Group

As in KIP-848, upgrading from a classic consumer group currently used in Kafka Streams to the new Streams group is possible by rolling the Streams clients assuming the Streams protocol is enabled on the brokers. When the first consumer of a Streams client using the new Streams rebalance protocol joins the group, the group is converted from a classic group to a streams group. When the last consumer of an Streams client using the new Streams rebalance protocol leaves the group, the group is converted back to a classic group. Note that the group epoch starts at the current group generation. During the migration, all the JoinGroup, SyncGroup and Heartbeat calls from the non-upgraded consumers are translated to the new Streams protocol.

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A more detailed description of this process can be found in KIP-848 in Section Supporting Online Consumer Group Upgrade.  An example of a migration:

Example

• classic group (generation=23)
  
  • A
  • B

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