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https://issues.apache.org/jira/browse/KAFKA-6520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17112118#comment-17112118
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Vince Mu commented on KAFKA-6520:
---------------------------------
I think the easiest and perhaps simplest way is to check if the stream client
is connected is to poll for whether the group coordinator is known in the
stream thread's consumer. However this would involve changes to the consumer
api.
However [~hachikuji] mentioned earlier in the [PR
|[https://github.com/apache/kafka/pull/6594]], that coordinator liveliness is
not enough to determine whether the streams client is disconnnected. Why is the
case?
> When a Kafka Stream can't communicate with the server, it's Status stays
> RUNNING
> --------------------------------------------------------------------------------
>
> Key: KAFKA-6520
> URL: https://issues.apache.org/jira/browse/KAFKA-6520
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Michael Kohout
> Priority: Major
> Labels: newbie, user-experience
>
> KIP WIP:
> [https://cwiki.apache.org/confluence/display/KAFKA/KIP-457%3A+Add+DISCONNECTED+status+to+Kafka+Streams]
> When you execute the following scenario the application is always in RUNNING
> state
>
> 1)start kafka
> 2)start app, app connects to kafka and starts processing
> 3)kill kafka(stop docker container)
> 4)the application doesn't give any indication that it's no longer
> connected(Stream State is still RUNNING, and the uncaught exception handler
> isn't invoked)
>
>
> It would be useful if the Stream State had a DISCONNECTED status.
>
> See
> [this|https://groups.google.com/forum/#!topic/confluent-platform/nQh2ohgdrIQ]
> for a discussion from the google user forum. This is a link to a related
> issue.
> -------------------------
> Update: there are some discussions on the PR itself which leads me to think
> that a more general solution should be at the ClusterConnectionStates rather
> than at the Streams or even Consumer level. One proposal would be:
> * Add a new metric named `failedConnection` in SelectorMetrics which is
> recorded at `connect()` and `pollSelectionKeys()` functions, upon capture the
> IOException / RuntimeException which indicates the connection disconnected.
> * And then users of Consumer / Streams can monitor on this metric, which
> normally will only have close to zero values as we have transient
> disconnects, if it is spiking it means the brokers are consistently being
> unavailable indicting the state.
> [~Yohan123] WDYT?
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