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Comment: Updated doc for ES Rolling upgrade to 7.17

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A rolling restart of the ES cluster may be needed to upgrade the Elasticsearch version or to perform maintenance on the server itself, such as an OS update or hardware change. This process keeps the cluster operational while taking nodes offline one at a time. Because Elasticsearch prefers to keep data fully replicated and evenly balanced, it must be made to pause rebalancing until the rolling restart completes.

This pausing is performed through ES settings changes, as recommended by Elasticsearch in the bolded links below. The essential process is this:

  1. Start maintenance mode by changing Change the ES settings to start maintenance mode.

  2. Complete the maintenance work (such as upgrading ES) and rolling restart. 

  3. Stop maintenance mode by restoring Restore the ES settings to stop maintenance mode.

Follow the steps in the Elasticsearch documentation, with this important addition for versions before Elasticsearch 7:specified below:

Info

ONLY for Elasticsearch Clusters Prior to Version 7

Set the discovery.zen.minimum_master_nodes value in the /etc/elasticsearch/elasticsearch.yml config file to be: (number of master-eligible-nodes/2, rounded down) + 1 when the elasticsearch cluster is first configured.
Verify the number is smaller than the number of currently available nodes. Run the following command now, to set that number to be <current_min_master_nodes>: (current number of master-eligible-nodes/2, rounded down) + 1 if not.

Code Block
languagebash
curl -s -XPUT 'http://ES_NODE:9200/_cluster/settings' \
	--data-binary '{"transient": {"discovery.zen.minimum_master_nodes" : "<current_min_master_nodes>"}}'

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Follow the Elasticsearch rolling restart procedure for the version:

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After maintenance is complete, restore discovery.zen.minimum_master_nodes to its original value, or adjust it based on the current number of expected available nodes after completing the rolling restart

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.

Code Block
languagebash
curl -s -XPUT 'http://ES_NODE:9200/_cluster/settings' \
	--data-binary '{"transient": {"discovery.zen.minimum_master_nodes" : "<original_min_master_nodes>"}}'

  1. Follow the Elasticsearch rolling restart procedure for the version:

    • ES Rolling Upgrades (7.17): Follow steps 1 and 2 (disable shard allocation and synced flush).
      Disable shard allocation with a curl like this:

      Code Block
      curl -X PUT "ES_NODE:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
  "persistent": {
    "cluster.routing.allocation.enable": "primaries"
  }
}
'

      Perform a Synced flush with a curl like this (optional):

      Code Block
      curl -X POST "ES_NODE:9200/_flush/synced?pretty"

  2. Stop the Elasticsearch node if you are shutting down the server for maintenance.

    Code Block
    systemctl stop elasticsearch

    Or, restart the service if you made configuration changes.

    Code Block
    systemctl restart elasticsearch

  3. After the server and service have started, you can re-enable shard allocation.

    Code Block
    curl -X PUT "ES_NODE:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
  "persistent": {
    "cluster.routing.allocation.enable": null
  }
}
'

  4. Monitor the cluster health and wait for the status column to switch to green. Once the node is green, all primary and replica shards have been allocated.

    Code Block
    curl -X GET "ES_NODE:9200/_cat/health?v=true&pretty"

    Monitor the recovery status if it is in yellow or red status.

    Code Block
    curl -X GET "ES_NODE:9200/_cat/recovery?pretty"