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Current state: Under discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: https://issues.apache.org/jira/browse/KAFKA-16891JIRA: here [Change the link from KAFKA-1 to your own ticket]

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

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Note that --group-type consumer  actually matches all groups whose protocol is "consumer" , and --group-type share  matches all groups whose type is Share. The filtering is done in the kafka-groups.sh  tool.

Here are some examples.

To list all of the groups:

$ bin/kafka-groups.sh --bootstrap-server localhost:9092 --list
old-consumer-group
new-consumer-group
connect-cluster
share-group

To describe all of the groups and their types:

$ bin/kafka-groups.sh --bootstrap-server localhost:9092 --describe
GROUP                   TYPE          PROTOCOL
old-consumer-group      Classic       consumer
new-consumer-group      Consumer      consumer
connect-cluster         Classic       connect
share-group             Share         share

To list all of the consumer groups:

$ bin/kafka-groups.sh --bootstrap-server localhost:9092 --list --group-type consumer
old-consumer-group
new-consumer-group

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$ bin/kafka-groups.sh --bootstrap-server localhost:9092 --describe --group-type consumer
GROUP                   TYPE          PROTOCOL
old-consumer-group      Classic       consumer
new-consumer-group      Consumer      consumer

kafka-consumer-groups.sh

For all operations which act on a single group, if that group exists but is not a consumer group, the command fails with a message indicating that the group type is incorrect, rather than the existing message that the group does not exist.

For example, if you try to describe a share group, the output will look like this:

$ bin/kafka-consumer-groups.sh --bootstrap-server localhost:9092 --describe --group SG1
Error: Group 'SG1' is not a consumer group.

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Also, for all operations which act on a single group, if that group exists but is not a share group, the command fails with a message indicating that the group type is incorrect, rather than the existing messages that the group does not exist.

For example, if you try to describe a consumer group, the output will look like this:

$ bin/kafka-share-groups.sh --bootstrap-server localhost:9092 --describe --group CG1
Error: Group 'CG1' is not a share group.

Proposed Changes

This KIP introduces a command-line tool for displaying all of the groups and their types.

Next, it introduces a way to create a share group administratively. If you create Kafka resources such as topics as part of deploying an application, you can now create share groups in the same way.

Finally, in situations where command-line tools are used to administer a group of the wrong type, you’ll now be told the group type is wrong, rather than the group does not exist.

Listing groups

The KIP introduces a new tool called kafka-groups.sh to show all of the groups in a cluster, their types and the protocols they use. This lets you see consumer groups, share groups, Kafka Connect cluster groups, and any other custom groups all together. It doesn't replace the specific tools for the different types of group, but it does shed light on what's actually going on for administrators. Note that this does not require any changes to the Kafka protocol. The information is already available, but not directly accessible by the administrator.

The ListGroups RPC response returns three pieces of information for each group: group ID, type and protocol. For the common types of group, here is what they mean:

The new kafka-groups.sh tool makes all of this information available.

Creating groups

Groups are created dynamically on first use. For example, when you connect the first consumer in a consumer group, the group coordinator creates the group as a consumer group. This is convenient, but it does mean that you need to ensure that different types of group use distinct group IDs or the results will be unpredictable. This is because the group type depends upon how the group was created, whether it was a consumer group member, a distributed Kafka Connect cluster, or whatever.

Today, you can create a consumer group administratively before the first member joins by resetting the offsets, such as like this:

$ bin/kafka-consumer-groups.sh --bootstrap-server localhost:9092 --reset-offsets --to-latest --group CG1 --topic T1 --execute

That’s a slightly contorted way to create a consumer group, but it does already exist and it is known. As a result, this KIP does not introduce a new way to create consumer groups.

For share groups, a new --create  option is added to the kafka-share-groups.sh  tool to create a share group. You can use --reset-offsets  in a similar way as consumer groups, but if you want to create a share group without specifying any topics, use --create  instead. Note that the starting offset of a share group comes from the group's group.share.auto.offset.reset  configuration property as introduced in KIP-932. This defaults to "latest" .

$ bin/kafka-share-groups.sh --bootstrap-server localhost:9092 --create --group SG1 

Compatibility, Deprecation, and Migration Plan

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