Why doesn't graylog2 display logs if one of the elasticsearch cluster nodes is unavailable?

Question

graylog

Testing graylog2. The following scheme is deployed on 4 virtual machines:
2 backends - graylog-server, mongodb (replica set), elasticsearch (master and data node)
2 frontends - keepalive, haproxy, mongodb (replica set arbiter ), elasticsearch (master node without data )
Everything works great except for the case when one of the elasticsearch data nodes is not available. As soon as the service is turned off, graylog stops displaying already collected logs and collecting new ones.
As far as I understand, in the case of two elasticsearch nodes, when one of the nodes drops out, the cluster should turn into yellow. For me, it immediately becomes red - At least one primary shard (and all of its replicas) is missing.
Plz tell me where to dig...

Answer 1

I figured it out... by default, the graylog-server config says:
elasticsearch_replicas = 0