How to Monitor Elasticsearch Cluster: Key Commands and Tips

To monitor an Elasticsearch cluster, use the _cluster/health API to check cluster status and the _nodes/stats API for detailed node metrics. You can also use tools like Kibana or Elastic Stack monitoring features for real-time insights.

Syntax

Elasticsearch provides REST APIs to monitor cluster health and node statistics.

• GET /_cluster/health: Returns overall cluster health status.
• GET /_nodes/stats: Provides detailed statistics about each node.
• GET /_cat/health: Shows a concise health summary in text format.

http

GET /_cluster/health
GET /_nodes/stats
GET /_cat/health?v

Example

This example shows how to check the cluster health and node stats using curl commands.

bash

curl -X GET "localhost:9200/_cluster/health?pretty"
curl -X GET "localhost:9200/_nodes/stats?pretty"

Output

{
  "cluster_name" : "my-cluster",
  "status" : "green",
  "number_of_nodes" : 3,
  "active_primary_shards" : 10,
  "active_shards" : 20,
  "relocating_shards" : 0,
  "initializing_shards" : 0,
  "unassigned_shards" : 0,
  "delayed_unassigned_shards" : 0,
  "number_of_pending_tasks" : 0,
  "number_of_in_flight_fetch" : 0,
  "task_max_waiting_in_queue_millis" : 0,
  "active_shards_percent_as_number" : 100.0
}

{
  "nodes" : {
    "node_id_1" : {
      "name" : "node-1",
      "indices" : {
        "docs" : {
          "count" : 10000,
          "deleted" : 100
        },
        "store" : {
          "size_in_bytes" : 123456789
        }
      },
      "jvm" : {
        "mem" : {
          "heap_used_in_bytes" : 104857600
        }
      }
    }
  }
}

Common Pitfalls

Common mistakes when monitoring Elasticsearch clusters include:

• Not checking cluster health regularly, which can delay detection of issues.
• Ignoring unassigned shards reported by _cluster/health.
• Using only _cat APIs without detailed stats, missing important metrics.
• Not securing API access, exposing sensitive cluster data.

Always combine health checks with node stats and use secured connections.

bash

curl -X GET "localhost:9200/_cluster/health"
# Wrong: ignoring unassigned shards
# Right: check unassigned shards count and investigate

curl -X GET "localhost:9200/_cluster/health?pretty"
# Check "unassigned_shards" field for issues

Quick Reference

API Endpoint	Purpose	Example Usage
/_cluster/health	Check overall cluster health status	GET /_cluster/health?pretty
/_nodes/stats	Get detailed node statistics	GET /_nodes/stats?pretty
/_cat/health	Show concise health summary	GET /_cat/health?v
/_cat/nodes	List nodes with basic info	GET /_cat/nodes?v

Key Takeaways

Use the _cluster/health API to monitor overall cluster status regularly.

Check _nodes/stats for detailed node performance and resource usage.

Watch for unassigned shards as a sign of cluster issues.

Secure your monitoring APIs to protect cluster data.

Combine API checks with tools like Kibana for real-time monitoring.