[jira] [Commented] (KAFKA-7610) Detect consumer failures in initial JoinGroup

["Boyang Chen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-7610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16682509#comment-16682509 ] 

Boyang Chen commented on KAFKA-7610:
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Thanks Jason for proposing this issue. I think in static membership ([KIP-345|https://cwiki.apache.org/confluence/display/KAFKA/KIP-345%3A+Introduce+static+membership+protocol+to+reduce+consumer+rebalances]) we should be able to address this issue by remembering the newly joined member's name, even after multiple disconnects we will still have the exact same member.

This by far I feel is the easiest solution since no matter what approach we eventually take, it requires authentication of client identity. I'm in favor of the approach 2 so far on dynamic membership, and the key point I'm trying to understand is what if the response message failed on the way, which will lead to another "unknown member" join for a new consumer as I suppose?

> Detect consumer failures in initial JoinGroup
> ---------------------------------------------
>
>                 Key: KAFKA-7610
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7610
>             Project: Kafka
>          Issue Type: Improvement
>            Reporter: Jason Gustafson
>            Priority: Major
>
> The session timeout and heartbeating logic in the consumer allow us to detect failures after a consumer joins the group. However, we have no mechanism to detect failures during a consumer's initial JoinGroup when its memberId is empty. When a client fails (e.g. due to a disconnect), the newly created MemberMetadata will be left in the group metadata cache. Typically when this happens, the client simply retries the JoinGroup. Every retry results in a new dangling member created and left in the group. These members are doomed to a session timeout when the group finally finishes the rebalance, but before that time, they are occupying memory. In extreme cases, when a rebalance is delayed (possibly due to a buggy application), this cycle can repeat and the cache can grow quite large.
> There are a couple options that come to mind to fix the problem:
> 1. During the initial JoinGroup, we can detect failed members when the TCP connection fails. This is difficult at the moment because we do not have a mechanism to propagate disconnects from the network layer. A potential option is to treat the disconnect as just another type of request and pass it to the handlers through the request queue.
> 2. Rather than holding the JoinGroup in purgatory for an indefinite amount of time, we can return earlier with the generated memberId and an error code (say REBALANCE_IN_PROGRESS) to indicate that retry is needed to complete the rebalance. The consumer can then poll for the rebalance using its assigned memberId. And we can detect failures through the session timeout. Obviously this option requires a KIP (and some more thought).



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