Monitoring Overlord/Index slots

I am trying to write some monitoring/alerting when our indexers start to fill up (or a indexer fails). I am using a statsd metrics emitter and I do not see a metric for this. I looked at the http endpoints and none of them return this info. I do see it in the overlord and coordinator console. Is there anyway to see how many remaining index slots I have?

Thanks!

you can use those endpoints overlord_ip_port/druid/indexer/v1/[pendingTasks, runningTasks completeTasks]

https://github.com/b-slim/druid/blob/4b3bd8bd630130fb852dfa3054bd9a60d507fd2b/indexing-service/src/main/java/io/druid/indexing/overlord/http/OverlordResource.java#L427-L427