[jira] [Commented] (KAFKA-13405) Kafka Streams restore-consumer fails to refresh broker IPs after upgrading Kafka cluster

["Matthias J. Sax (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-13405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17435163#comment-17435163 ] 

Matthias J. Sax commented on KAFKA-13405:
-----------------------------------------

Thanks for reporting this issue.
{quote} * None of the original broker IPs are valid/accessible after the upgrade (as expected){quote}
Why would this be expected? If you do a rolling upgrade, IP address should stay the same?
{quote} * Restart our applications after upgrading our Kafka cluster{quote}
As all IP addresses changed, you cannot simple restart the application without updating the `bootstrap.server` config, right? Otherwise, the "main consumers" won't be able to connect to the broker cluster either.

The difference between the main consumer and the restore consumer is, that the main consumer is always active, and thus during a broker upgrade can update its metadata step by step. However, the restore consumer is only used during restore (or if you have standby tasks enabled) and thus, does not actively communicate with the cluster and thus does not update its metadata. Also note, that if your application crashed and would restart, the main consumer (using the old `bootstrap.server` config) would also not be able to reconnect to the cluster.

Overall, I am not sure if we can resolve this issue, and to some extend it seems like a user error: because you changed all IPs, you also need to update the `bootstrap.server` config for all clients (which requires a bounce of all clients). And as a matter of fact, it seems that updating the config and restarting Kafka Streams resolved the issue. In general, a cluster upgrade should not even change IP addresses though.

> Kafka Streams restore-consumer fails to refresh broker IPs after upgrading Kafka cluster
> ----------------------------------------------------------------------------------------
>
>                 Key: KAFKA-13405
>                 URL: https://issues.apache.org/jira/browse/KAFKA-13405
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 2.8.0, 2.7.1
>            Reporter: Daniel O'Halloran
>            Priority: Critical
>         Attachments: KafkaConfig.txt, KafkaLogs.txt
>
>
> *+Description+*
> After upgrading our Kafka clusters from 2.7 to 2.8 the Streams restore-consumers never update their broker IPs.
> The applications continue to process events as normal, until there is a rebalance.
> Once a rebalance occurs the restore consumers attempts to connect to the old brokers IPs indefinitely and the streams tasks never go back into a RUNNING state.
> We were able to replicate this behaviour with kafka-streams client libraries 2.5.1, 2.7.1 and 2.8.0
>  
> *+Steps to reproduce+*
>  # Upgrade brokers from Kafka 2.7 to Kafka 2.8
>  # Ensure old brokers are completely shut down
>  # Trigger a rebalance of a streams application
>  
> *+Expected result+*
>  * Application rebalances as normal
>  
> *+Actual Result+*
>  * Application cannot restore its data
>  * restore consumer tries to connect to old brokers indefinitely
>  
> *+Observations+*
>  * The cluster metadata was updated on all stream consumer threads during the broker upgrade (multiple times) as the new brokers were brought online (corresponding to leader election occurring on the subscribed partitions), however no cluster metadata was logged on the restore-consumer thread.
>  * None of the original broker IPs are valid/accessible after the upgrade (as expected)
>  * No partition rebalance occurs during the kafka upgrade process.
>  * When the first re-balance was triggered after upgrade, the restore-consumer loops failing to connect on each of the 3 original IPs, but none of the new broker IPs.
>  
> *+Workaround+*
>  * Restart our applications after upgrading our Kafka cluster



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