https://www.elastic.co/guide/en/elasticsearch/reference/current/modules-discovery-zen.html#unicast

The documentation around discovery.zen.ping.unicast.hosts doesn't specify what kind of hosts should be added. Is it all nodes? All master nodes? At least one master? Is there a recommended minimum?

There is no information as to when to update this list either or when the list of hosts are actually used (only at start? at any master election?).

Perhaps a link to https://www.elastic.co/guide/en/elasticsearch/reference/current/important-settings.html#unicast.hosts and expand the explanation here?