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

Describe the problems you are trying to solve.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Currently, there exists a kafka.server:type=MetadataLoader,name=CurrentMetadataVersion  metric which tells the operator the metadata version feature level for every node in a cluster. However, now that there several features with support beyond the metadata.version  feature. Adding a metric to display those features' levels would be helpful for monitoring upgrade/downgrade scenarios for clusters using those features.

Public Interfaces

Monitoring

Add a metric for each production feature (i.e. kraft.version , transaction.version , group.version , eligible.leader.replicas.version , and share.version ).

This can be accomplished via one generic "feature level" metric that is tagged by feature. Using a generic metric allows for new production features to automatically expose their feature level going forward. 

The default value of this metric should be the default value of the featureDescribe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

We might want to deprecate the kafka.server:type=MetadataLoader,name=CurrentMetadataVersion metric since this per-feature tagged metric can also expose the current metadata version.

Test Plan

We will add junit tests to verify the new metrics.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?

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.