Warning in Logstash log after fresh start

Elastic Stack Logstash
1

Hi there.

I working on upgrade to newer Logstash version (9.1.3) from oldest used one (8.9.0). It seems, that now it is working correctly, but I am struggling with some warning messages:

[2025-09-08T13:33:55,354][WARN ][logstash.outputs.opensearch] Restored connection to OpenSearch instance {:url=>"https://REDACTED.local:9200/"}

This is bug in OpenSearch output plugin and should be INFO. Nothing harmful. We using Logstash with the plugin in the state several years and no problem.

[2025-09-08T13:33:56,447][WARN ][org.apache.kafka.clients.CommonClientConfigs] Disabling exponential reconnect backoff because reconnect.backoff.ms is set, but reconnect.backoff.max.ms is not.

This look like another bug, but in Logstash or Kafka plugin. Based on the documentation, the attribute reconnect.backoff.ms is possible set in Logstash config for Kafka, but attribute reconnect.backoff.max.ms isnt possible to set, due to missing functionality.

I would like to kindly ask you about the information, how to handle the warning regarding the Kafka plugin? It isnt really harmful and we can consider it as a information?

Thank you!

2

Is that just at startup? There is code in the elasticsearch output that passes a parameter to healthcheck! to determine whether this is logged as INFO (during startup) or WARN (when it has to reconnect after losing a connection. The opensearch plugin does not. Feel free to open an issue in their github repo.

Are you saying this is new? This error appears to have been added in the KIP-580 implementation in Kafka 3.7.0, which I think was picked up in November 2024, logstash 8.9.0 is older than that.

Bug? Maybe. You’ll get reconnect retries every reconnect.backoff.ms (it resets the max to this when it logs the error). I think it gives you the behaviour you had with the older Kafka version, but I don’t have time to dig into the old Kafka code to be sure.

4

Yop, previous Logstash version emitted by the OpenSearch project have the same problem.
OK, thank you for feedback!

New for us :). Yop, we still using old Kafka version (3.8.0).
Sorry for confusion, let me accurate it: The error message is new for me, when I attempting to using Logstash 9.1.3 with Kafka 3.8.0.
Anyway, thank you, I have upgrading Kafka in tasks list as well, so there is a chance, that the error message will dissapeared after using newer Kafka version.

Thank you for feedback. I would like to evade situation, when Kafka will be under presure and will have some troubles to communicate with Logstash.

Thank you very much, I got all answers, what I need :). I really appreaciate it!