rolling_upgrade.asciidoc

Rolling upgrades

A rolling upgrade allows an Elasticsearch cluster to be upgraded one node at a time so upgrading does not interrupt service. Running multiple versions of Elasticsearch in the same cluster beyond the duration of an upgrade is not supported, as shards cannot be replicated from upgraded nodes to nodes running the older version.

Rolling upgrades can be performed between minor versions. Elasticsearch 6.x supports rolling upgrades from Elasticsearch 5.6. Upgrading from earlier 5.x versions requires a full cluster restart. You must reindex to upgrade from versions prior to 5.x.

To perform a rolling upgrade:

1. Disable shard allocation.

   disable-shard-alloc.asciidoc

2. Stop non-essential indexing and perform a synced flush. (Optional)

   While you can continue indexing during the upgrade, shard recovery is much faster if you temporarily stop non-essential indexing and perform a synced-flush.

   synced-flush.asciidoc

3. Stop any machine learning jobs that are running. See {xpack-ref}/stopping-ml.html[Stopping Machine Learning].

4. Shut down a single node.

   shut-down-node.asciidoc

5. Upgrade the node you shut down.

   upgrade-node.asciidoc set-paths-tip.asciidoc

6. Upgrade any plugins.

   Use the elasticsearch-plugin script to install the upgraded version of each installed Elasticsearch plugin. All plugins must be upgraded when you upgrade a node.

7. Start the upgraded node.

   Start the newly-upgraded node and confirm that it joins the cluster by checking the log file or by submitting a _cat/nodes request:

   GET _cat/nodes

8. Reenable shard allocation.

   Once the node has joined the cluster, remove the cluster.routing.allocation.enable setting to enable shard allocation and start using the node:

   PUT _cluster/settings
   {
     "persistent": {
       "cluster.routing.allocation.enable": null
     }
   }

9. Wait for the node to recover.

   Before upgrading the next node, wait for the cluster to finish shard allocation. You can check progress by submitting a _cat/health request:

   GET _cat/health

   Wait for the status column to switch from yellow to green. Once the node is green, all primary and replica shards have been allocated.

   Important

   During a rolling upgrade, primary shards assigned to a node running the new version cannot have their replicas assigned to a node with the old version. The new version might have a different data format that is not understood by the old version. If it is not possible to assign the replica shards to another node (there is only one upgraded node in the cluster), the replica shards remain unassigned and status stays yellow. In this case, you can proceed once there are no initializing or relocating shards (check the init and relo columns). As soon as another node is upgraded, the replicas can be assigned and the status will change to green.

   Shards that were not sync-flushed might take longer to recover. You can monitor the recovery status of individual shards by submitting a _cat/recovery request:

   GET _cat/recovery

   If you stopped indexing, it is safe to resume indexing as soon as recovery completes.

10. Repeat

    When the node has recovered and the cluster is stable, repeat these steps for each node that needs to be updated.

11. Restart machine learning jobs.

Important

During a rolling upgrade, the cluster continues to operate normally. However, any new functionality is disabled or operates in a backward compatible mode until all nodes in the cluster are upgraded. New functionality becomes operational once the upgrade is complete and all nodes are running the new version. Once that has happened, there’s no way to return to operating in a backward compatible mode. Nodes running the previous major version will not be allowed to join the fully-updated cluster. In the unlikely case of a network malfunction during the upgrade process that isolates all remaining old nodes from the cluster, you must take the old nodes offline and upgrade them to enable them to join the cluster.