elasticsearch/docs/reference/upgrade/preparing_to_upgrade.asciidoc

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=== Preparing to upgrade

It is important to prepare carefully before starting an upgrade. Once you have
started to upgrade your cluster to version {version} you must complete the
upgrade. As soon as the cluster contains nodes of version {version} it may make
changes to its internal state that cannot be reverted. If you cannot complete
the upgrade then you should discard the partially-upgraded cluster, deploy an
empty cluster of the version before the upgrade, and restore its contents from
a snapshot.

Before you start to upgrade your cluster to version {version} you should do the
following.

. Check the <<deprecation-logging, deprecation log>> to see if you are using any
deprecated features and update your code accordingly.

. Review the <<breaking-changes,breaking changes>> and make any necessary
changes to your code and configuration for version {version}.

. If you use any plugins, make sure there is a version of each plugin that is
compatible with {es} version {version}.

. Test the upgrade in an isolated environment before upgrading your production
cluster.

. <<modules-snapshots,Back up your data by taking a snapshot!>>