Health of the cluster

Elasticsearch provides various APIs for operational management of clusters and nodes. One of the important APIs is cluster API. In the previous section, we started a single-node cluster. We can check the health of the cluster using the cluster API as follows:

http://127.0.0.1:9200/_cluster/health?pretty

The pretty flag at the end of the URL makes the JSON response more readable. The response from the cluster API is shown next:

{
   "cluster_name": "es-dev",
"status": "green",
   "timed_out": false,
   "number_of_nodes": 1,
   "number_of_data_nodes": 1,
   "active_primary_shards": 0,
   "active_shards": 0,
   "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
 }

You can tell from the JSON response that the current status of the cluster is green (the cluster status...