i have read it in other blog this same issues but not getting exact reason for this what casing this error
2016-09-30 21:36:51,098 [Hashed wheel timer #1] WARN c.m.tranquility.beam.ClusteredBeam - Emitting alert: [anomaly] Failed to propagate events: druid:overlord/test_topic
{
"eventCount" : 1,
"timestamp" : "2016-09-30T21:00:00.000Z",
"beams" : "MergingPartitioningBeam(DruidBeam(interval = 2016-09-30T21:00:00.000Z/2016-09-30T22:00:00.000Z, partition = 0, tasks = [index_realtime_test_topic_2016-09-30T21:00:00.000Z_0_0/test_topic-021-0000-0000; index_realtime_test_topic_2016-09-30T21:00:00.000Z_0_1/test_topic-021-0000-0001]), DruidBeam(interval = 2016-09-30T21:00:00.000Z/2016-09-30T22:00:00.000Z, partition = 1, tasks = [index_realtime_test_topic_2016-09-30T21:00:00.000Z_1_0/test_topic-021-0001-0000; index_realtime_test_topic_2016-09-30T21:00:00.000Z_1_1/test_topic-021-0001-0001]))"
}
com.twitter.finagle.NoBrokersAvailableException: No hosts are available for disco!firehose:druid:overlord:test-prachi-021-0001-0000, Dtab.base=[], Dtab.local=[]
at com.twitter.finagle.NoStacktrace(Unknown Source) ~[na:na]