Status

Current state: Draft

Discussion thread: here

JIRA: KAFKA-3853

Released: <Kafka Version>

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

Motivation

KAFKA-3853 asks for an improvement to the new-consumer option of the consumer group command. This command, when passed a consumer group that has no consumer (i.e., when the group state is Empty), currently reports an error indicating that there is no active member:

$ bin/kafka-consumer-groups.sh --new-consumer --bootstrap-server localhost:9092 --describe --group group1
Note: This will only show information about consumers that use the Java consumer API (non-ZooKeeper-based consumers).
Error: Consumer group 'group1' has no active members.

The requested improvement is returning offsets within the group (and leaving the owner column empty) instead of returning the error message above. The error message can still be printed to to stderr as a warning.

When the group is Stable (i.e. when there are active consumers in the group), the offsets associated with the group are returned as part of the info returned for each consumer in the group in terms of a ConsumerSummary record. But there is no ConsumerSummary record if there is no consumer in the group, and therefore, in that scenario a different method is required for extracting those offsets.

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

Describe 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

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.