How to identify the elected master node in Elasticsearch

Identifying the elected master node shows which Elasticsearch node is currently publishing cluster-state changes. Operators use this check during rolling restarts, node-loss incidents, and shard allocation reviews because a missing or frequently changing master can delay metadata updates, node joins, and management API responses.

The _cat/master endpoint returns the elected node ID, host, IP address, and node name in a compact table for terminal checks. The _cat/nodes endpoint can then show the same node with * in the master column and expose whether each node is master-eligible through the compact node.role flags.

Run the request against an Elasticsearch HTTP endpoint that belongs to the cluster being inspected. Secured deployments usually require HTTPS, authentication, and a trusted CA, while the cluster-state API should stay a narrow diagnostic cross-check because Elastic warns that repeated broad cluster-state requests can stress larger clusters.

1. Query the elected master node from an Elasticsearch HTTP endpoint.

   $ curl -sS --fail "http://localhost:9200/_cat/master?v&h=id,host,ip,node"
   id                     host       ip         node
   JndZsMgTSmukbYqEPosNHg 192.0.2.40 192.0.2.40 es-master-01

   The request needs the monitor cluster privilege. On secured clusters, switch to the cluster's https:// endpoint and add the CA trust plus authentication method already used by operators.

   A 401 or 403 response indicates missing credentials or insufficient privilege, while 503 or master_not_discovered_exception indicates the cluster does not currently have an elected master.

2. Cross-check the same node against the cluster node list.

   $ curl -sS --fail "http://localhost:9200/_cat/nodes?v&full_id=true&h=id,name,ip,node.role,master"
   id                     name         ip         node.role   master
   JndZsMgTSmukbYqEPosNHg es-master-01 192.0.2.40 cdfhilmrstw *
   R7lPvJ2vTMevQW9ydT8wUQ es-data-01   192.0.2.41 cdfhilmrstw -
   Nw2sZx43QZe3nG5kY9zK7w es-data-02   192.0.2.42 cdfhilmrstw -

   The master column shows * on the elected master and - on other joined nodes. The node.role column includes m on master-eligible nodes and v on voting-only nodes, which can vote but cannot become the elected master.

   Related: How to check Elasticsearch node stats

3. Confirm the elected node ID from cluster state only when a JSON cross-check is needed.

   $ curl -sS --fail "http://localhost:9200/_cluster/state/master_node?filter_path=cluster_name,master_node&pretty"
   {
     "cluster_name" : "search-cluster",
     "master_node" : "JndZsMgTSmukbYqEPosNHg"
   }

   Using filter_path=cluster_name,master_node keeps the diagnostic response narrow. Elastic documents the cluster-state API as an internal diagnostic surface, so do not use it as a frequent monitoring poll.

   Related: How to check Elasticsearch cluster formation