Re-Index Billions of Documents in Elastic-Search from different Cluster:

• We can use the reindex API to migrate indices data from one cluster to another cluster.
• Elasticsearch provides backward compatibility support that enables indices from the previous major version to be upgraded to the current major version

Whitelist old cluster Node:

• Setup a new cluster.
• Added below property in one of the co-ordinators node.

reindex.remote.whitelist: old_cluster_node:9200

• Above property whitelist old_cluster_node IP to reindex data from old cluster to new.
• Set above property in elasticsearch.yml.
• And restart the node where you have added above property.
• This property does not need to be added to all nodes of the cluster, only node where you are going to hit the Reindex API.

Re-Index Data:

• Create an index of the appropriate mappings and settings.
• Set the refresh_interval to -1 and set number_of_replicas to 0 for faster reindexing.
• Refresh Interval stops data to index and the number of replicas will stop replication and shard allocations which take huge time.
• We can see the from the below example

curl --location --request PUT '${NEW_CLUSTER_NODE_IP}/$I{INDEX_NAME}/_settings' \
--header 'Content-Type: application/json' \
--data-raw '{
               {
                   "index" : {
                     "refresh_interval" : -1,
                      "number_of_replicas" : 0
                   }
               }
       }'

• Now we use reindex API to start re-indexing
• If you run the reindex job in the background by setting wait_for_completion to false, the reindex request returns a task_id you can use to monitor the progress of the reindex job with the task API: GET _tasks/TASK_ID.

curl --location --request PUT '${NEW_CLUSTER_NODE_IP}/_reindex?wait_for_completion=false' \
--header 'Content-Type: application/json' \
--data-raw '{
          "source": {
             "remote": {
                   "host": "${PRIMARY_SERVER_URL}",
                   "socket_timeout": "5m",
                   "connect_timeout": "5m"
               },
           "index": "${OLD_INDEX_NAME}"
        },
         "dest": {
              "index": "${NEW_INDEX_NAME}"
       }
   }'

Parameter Explanations:

host: The REST endpoint of the remote cluster.

socket_timeout: Time UnitThe wait time for socket reads (default 30s).

connect_timeout: Time UnitThe wait time for remote connection timeouts (default 30s)

• After reindexing completed:

Set the refresh_interval to 10s and set number_of_replicas to 2

curl --location --request PUT '${NEW_CLUSTER_NODE_IP}/$I{INDEX_NAME}/_settings' \
--header 'Content-Type: application/json' \
--data-raw '{
{
         "index" : {
           "refresh_interval" : 10s,
           "number_of_replicas" : 3
        }
      }
}'

Happy Learning!!

Thanks