I have faced a similar issue. Looks like maybe the elasticsearch_discovery_zen_ping_unicast_hosts configuration is incorrect. Please look at that. Anyways also have created the below issue https://github.com/Graylog2/graylog2-server/issues/2929 as the logs are misleading.
> > > > > > > > > > > > > > > > > > > > -- You received this message because you are subscribed to the Google Groups "Graylog Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/graylog2/634ba5b3-9f1f-4c0a-9231-6be201529ba6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
