Status

Current state: "Under Discussion"

Discussion thread: TODO

JIRA: Unable to render Jira issues macro, execution error.

Released: 3.0.0

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

Motivation

Since Kafka 2.4.0, it is possible to rely on the broker default replication factor setting when creating a topic (cf KIP-464: Defaults for AdminClient#createTopic). Kafka Streams did not adapt this new feature yet, due to backward compatibility concern. However, it puts some burden on users to change the Kafka Streams default replication.factor config of 1 when they put an application into production. While user are already able to change the config to -1  if their brokers are on 2.4.0 or newer version, it's still an additional config they need to take care of.

Public Interfaces

The default config of replication.factor should be changes.

Proposed Changes

We propose the change the default value of StreamsConfig.REPLICATION_FACTOR_CONFIG from 1 to -1 (meaning use broker default).

Compatibility, Deprecation, and Migration Plan

This change may impact users running Kafka Streams applications against older brokers, i.e., 2.3 or older that don't support the -1 config. For those uses, they would need to change the default before they can start a (new) application.

Note: if an existing application is upgrade, users won't be affected, because if internal replication/changleog topics exist already, no create topic request would be sent anyway. Only if a new application is deployed, or if an existing application is reset, and thus repartition/changelog topics would need to be created users might be affected. Because the application won't startup for this case, the impact is minor and can be considered non-critical. Applications already running in production won't break.

We also believe that 2.3.0 broker a sufficiently old such that not too many user may be affected, and we want to take to opportunity of a major release to make this change (as it's technically breaking backward compatibility).

Test Plan

Regular unit testing is sufficient to ensure that users get a descriptive error message if they hit this client/server incompatibility.

Rejected Alternatives

N/A