There are two important discovery and cluster formation settings that should be configured before going to production so that nodes in the cluster can discover each other and elect a master node.
Out of the box, without any network configuration, Elasticsearch will bind to the available loopback addresses and will scan local ports 9300 to 9305 to try to connect to other nodes running on the same server. This provides an auto-clustering experience without having to do any configuration.
When you want to form a cluster with nodes on other hosts, you should use the
discovery.seed_hosts setting to provide a list of other nodes in the cluster
that are master-eligible and likely to be live and contactable in order to seed
the discovery process. This setting value
should be a YAML sequence or array of the addresses of all the master-eligible
nodes in the cluster. Each address can be either an IP address or a hostname
which resolves to one or more IP addresses via DNS.
The port is optional and usually defaults to
If a hostname resolves to multiple IP addresses then the node will attempt to discover other nodes at all resolved addresses.
IPv6 addresses must be enclosed in square brackets.
If your master-eligible nodes do not have fixed names or addresses, use an alternative hosts provider to find their addresses dynamically.
When you start a brand new Elasticsearch cluster for the very first time, there
is a cluster bootstrapping step, which
determines the set of master-eligible nodes whose votes are counted in the very
first election. In development mode, with no discovery
settings configured, this step is automatically performed by the nodes
themselves. As this auto-bootstrapping is inherently
unsafe, when you start a brand new cluster in production
mode, you must explicitly list the master-eligible nodes whose votes should be
counted in the very first election. This list is set using the
cluster.initial_master_nodes setting. You should not use this setting when
restarting a cluster or adding a new node to an existing cluster.
The initial master nodes should be identified by their