Status

Current state: Under Discussion

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

Motivation

We have 2 methods in AdminClient  for updating config, alterConfigs  and incrementalAlterConfigs , the former has many restrictions and has been deprecated from 2.3.0. However, It's still used in ConfigCommand  to update broker config and is resulting in a bug

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Note that I'm only changing the way we updating broker configs, user/topic/client-metrics configs are already being updated using incrementalAlterConfigs

Public Interfaces

kafka-configs.sh

1. Adding new options --disable-incremental , which is used for new client to connect to older servers before 2.3.0 when updating broker configs.

Proposed Changes

1. --disable-incremental is only makes sense when used together with (--alter) and (--broker <broker-id>)/(--entity-types brokers), or it will be ignored.
2. --disable-incremental is only makes sense when used together with (--bootstrap-server)/(bootstrap-controller), we are leaving zookeeper case unchanged.
3. use AdminClient.incrementalAlterConfigs without --disable-incremental flag when alter broker configs, which will fail if the broker is before 2.3.0.

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1. Use kafka-configs.sh to set log.cleaner.threads=2, the client will send it to server using AdminClient.incrementalAlterConfigs(), the broker will merge the old snapshot( {} ) with delta and save the new snapshot( {log.cleaner.threads=2} ) to metadata storage.
2. Use kafka-configs.sh to set background.threads=1, the client will send it to server using AdminClient.incrementalAlterConfigs(), the broker will merge the old snapshot( {log.cleaner.threads=2} ) with delta and got the new snapshot ({log.cleaner.threads=2, background.threads=1 }) to metadata storage.

The result is expected to be the same for both way, except that we can avoid some issues for AdminClient.alterConfigs().

Compatibility, Deprecation, and Migration Plan

There will be a backward compatibility problem here since incrementalAlterConfigs  is added from 2.3.0, we add a --disable-incremental option for older client to do smooth migration.

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Documentation Plan

What will the impact be on the documentation? List any affected areas/files. 

Rejected Alternatives

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new client tool with older server can be tested locally and using test cases.

Documentation Plan

There are some api changes and we should document about kafka-configs.sh change list

Rejected Alternatives

1. We fallback to using alterConfigs automatically if incrementalAlterConfigs is not supported, we need to unify the semantics if we want to do this heuristically, so we choose to give this privilege to users by add --disable-incremental.