I'm working on some monitoring tools for Kafka, and I've seen a couple of
clusters get into a state where ClientUtils.fetchTopicMetadata will show
that not all replicas are in the ISR.
At the same time, ZkUtils.getLeaderIsrAndEpochForPartition will show that
all all partitions are in the ISR, and
MBean will report 0.
What's going on? Is there something wrong with my controller, or should I
not be paying attention to ClientUtils.fetchTopicMetadata?