Streams uses three consumer APIs that can block infinite: commitSync(), committed(), and position(). Also KafkaProducer#send() can block. If EOS is enabled, KafkaProducer#initTransactions() also used to block (fixed in
KAFKA-6446) and we should double check the code if we handle this case correctly.
If we block within one operation, the whole StreamThread would block, and the instance does not make any progress, becomes unresponsive (for example, KafkaStreams#close() suffers), and we also might drop out of the consumer group.
Thanks to [KIP-266|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=75974886,] the Consumer now has non-blocking variants that we can use, but the same is not true of Producer. We can add non-blocking variants to Producer as well, or set the appropriate config options to set the max timeout.
Of course, we'd also need to be sure the catch the appropriate timeout exceptions.