Kafka: A consumer poll loop must not block

Slow work inside the loop trips max.poll.interval.ms and gets the consumer evicted.

Code

// Wrong: 30 seconds of work per record
for (var r : records) { slowHttpCall(r); }

// Right: hand off, or reduce the batch
props.put(ConsumerConfig.MAX_POLL_RECORDS_CONFIG, 10);
// or pause()/resume() around long work

Output

Consumer group is rebalancing, the last poll was 312s ago
(max.poll.interval.ms is 300000)