[KAFKA-5736] Improve error message in Connect when all kafka brokers are down

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 0.11.0.0
• Component/s: connect
• Assignee: Konstantine Karantasis
• Reporter: Konstantine Karantasis
• Reviewer: Jason Gustafson
• Created: 15/Aug/17 22:24
• Updated: 17/Feb/19 18:59

Description

Currently when all the Kafka brokers are down, Kafka Connect is failing with a pretty unintuitive message when it tries to, for instance, reconfigure tasks.

Example output:

[2017-08-15 19:12:09,959] ERROR Failed to reconfigure connector's tasks, retrying after backoff: (org.apache.kafka.connect.runtime.distributed.DistributedHerder)
java.lang.IllegalArgumentException: CircularIterator can only be used on non-empty lists
    at org.apache.kafka.common.utils.CircularIterator.<init>(CircularIterator.java:29)
    at org.apache.kafka.clients.consumer.RoundRobinAssignor.assign(RoundRobinAssignor.java:61)
    at org.apache.kafka.clients.consumer.internals.AbstractPartitionAssignor.assign(AbstractPartitionAssignor.java:68)
    at 

... (connector code)

    at org.apache.kafka.connect.runtime.Worker.connectorTaskConfigs(Worker.java:230)

The error message needs to be improved, since its root cause is the absence kafka brokers for assignment.