kafka exporter should give the possibility to exclude topic

[nicolasblaye]

I tried to use kafka_exporter on my newly created kafka. We have 3 brokers with only a handful of consumers. Because of that, not every partition is used in the __consumer_offsets topic. When I try to get the metrics, it takes a lot of time because it tries to connect to every partition leader and fails for the empty one with

ERRO[0081] Cannot get leader of topic __consumer_offsets partition 31: kafka server: In the middle of a leadership election, there is currently no leader for this partition and hence it is unavailable for writes.  source="kafka_exporter.go:275"
ERRO[0083] Cannot get current offset of topic __consumer_offsets partition 31: kafka server: In the middle of a leadership election, there is currently no leader for this partition and hence it is unavailable for writes.  source="kafka_exporter.go:284"
ERRO[0085] Cannot get oldest offset of topic __consumer_offsets partition 31: kafka server: In the middle of a leadership election, there is currently no leader for this partition and hence it is unavailable for writes.  source="kafka_exporter.go:296"

I saw that we can filter topic we want to listen to, using a regex, so I tried --topic.filter='^(?!__consumer_offsets).*$', but this is not go regex syntax so it failed with invalid or unsupported Perl syntax: (?!

It could be nice to instead have an exclusion mechanism, or to have a workaround for empty partition with no leader.

[danielqsj]

thanks, closed by #379