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Rolling upgrades

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Rolling upgrades

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A rolling upgrade allows the Elasticsearch cluster to be upgraded one node at a time, with no downtime for end users. Running multiple versions of Elasticsearch in the same cluster for any length of time beyond that required for an upgrade is not supported, as shards will not be replicated from the more recent version to the older version.

Consult this table to verify that rolling upgrades are supported for your version of Elasticsearch.

To perform a rolling upgrade:

Disable shard allocation

When you shut down a node, the allocation process will wait for one minute before starting to replicate the shards that were on that node to other nodes in the cluster, causing a lot of wasted I/O. This can be avoided by disabling allocation before shutting down a node:
```
PUT _cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "none"
  }
}
```
Stop non-essential indexing and perform a synced flush (Optional)

You may happily continue indexing during the upgrade. However, shard recovery will be much faster if you temporarily stop non-essential indexing and issue a synced-flush request:
```
POST _flush/synced
```
A synced flush request is a “best effort” operation. It will fail if there are any pending indexing operations, but it is safe to reissue the request multiple times if necessary.
Stop and upgrade a single node

Shut down one of the nodes in the cluster before starting the upgrade.

When using the zip or tarball packages, the config, data, logs and plugins directories are placed within the Elasticsearch home directory by default.

It is a good idea to place these directories in a different location so that there is no chance of deleting them when upgrading Elasticsearch. These custom paths can be configured with the path.conf, path.logs, and path.data settings, and using ES_JVM_OPTIONS to specify the location of the jvm.options file.

The Debian and RPM packages place these directories in the appropriate place for each operating system.

To upgrade using a Debian or RPM package:
- Use rpm or dpkg to install the new package. All files should be placed in their proper locations, and config files should not be overwritten.
To upgrade using a zip or compressed tarball:
- Extract the zip or tarball to a new directory, to be sure that you don’t overwrite the config or data directories.
- Either copy the files in the config directory from your old installation to your new installation, or set the environment variable ES_JVM_OPTIONS to the location of the jvm.options file and use the -E path.conf= option on the command line to point to an external config directory.
- Either copy the files in the data directory from your old installation to your new installation, or configure the location of the data directory in the config/elasticsearch.yml file, with the path.data setting.
Upgrade any plugins

Elasticsearch plugins must be upgraded when upgrading a node. Use the elasticsearch-plugin script to install the correct version of any plugins that you need.
Start the upgraded node

Start the now upgraded node and confirm that it joins the cluster by checking the log file or by checking the output of this request:
```
GET _cat/nodes
```
Reenable shard allocation

Once the node has joined the cluster, reenable shard allocation to start using the node:
```
PUT _cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "all"
  }
}
```
Wait for the node to recover

You should wait for the cluster to finish shard allocation before upgrading the next node. You can check on progress with the _cat/health request:
```
GET _cat/health
```
Wait for the status column to move from yellow to green. Status green means that all primary and replica shards have been allocated.

During a rolling upgrade, primary shards assigned to a node with the higher version will never have their replicas assigned to a node with the lower version, because the newer version may have a different data format which is not understood by the older version.

If it is not possible to assign the replica shards to another node with the higher version — e.g. if there is only one node with the higher version in the cluster — then the replica shards will remain unassigned and the cluster health will remain status yellow.

In this case, check that there are no initializing or relocating shards (the init and relo columns) before proceding.

As soon as another node is upgraded, the replicas should be assigned and the cluster health will reach status green.

Shards that have not been sync-flushed may take some time to recover. The recovery status of individual shards can be monitored with the _cat/recovery request:
```
GET _cat/recovery
```
If you stopped indexing, then it is safe to resume indexing as soon as recovery has completed.
Repeat

When the cluster is stable and the node has recovered, repeat the above steps for all remaining nodes.

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