Consumer sporadically doesn't receive messages when client.id is set

[mrubin]

Versions used

Akka version: 2.6.7
Alpakka Kafka version: 2.0.4
Kafka version: 2.6.x

Since switching from the Kafka Java SDK to Alpakka Kafka (no other changes), we have noticed that messages are sporadically not sent to the consumer. That is, our consumer misses processing some messages. Experimentally, it seems that what has made a difference is not setting "client.id". When setting "client.id", we would observe the sporadic "missed messages" behavior, and when not setting "client.id", we have been unable to reproduce the problem.

This makes no sense, as all available Kafka/Confluent/Stack Overflow/etc. documentation/notes about the client.id setting is along the lines of: “this setting has no functional effect, it's only used to tag requests so they can be matched in the broker's log if needed.”

Has anyone else experienced this issue?

[seglo]

That's very strange. Do you observe any issues in your logs? Try enabling DEBUG logging.