Important discovery and cluster formation settings

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.

discovery.seed_hosts

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 should be a list 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.

If your master-eligible nodes do not have fixed names or addresses, use an alternative hosts provider to find their addresses dynamically.

cluster.initial_master_nodes

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.

discovery.seed_hosts:
   - 192.168.1.10:9300
   - 192.168.1.11 
   - seeds.mydomain.com 
   - [0:0:0:0:0:ffff:c0a8:10c]:9301 
cluster.initial_master_nodes: 
   - master-node-a
   - master-node-b
   - master-node-c

The port is optional and usually defaults to 9300, but this default can be overridden by certain settings.

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.

The initial master nodes should be identified by their node.name, which defaults to their hostname. Make sure that the value in cluster.initial_master_nodes matches the node.name exactly. If you use a fully-qualified domain name such as master-node-a.example.com for your node names then you must use the fully-qualified name in this list; conversely if node.name is a bare hostname without any trailing qualifiers then you must also omit the trailing qualifiers in cluster.initial_master_nodes.

For more information, see Bootstrapping a cluster and Discovery and cluster formation settings.