elasticsearch/docs/reference/upgrade.asciidoc

[[setup-upgrade]]
= Upgrade {es}

{es} clusters can usually be upgraded one node at a time so upgrading does not
interrupt service. For upgrade instructions, refer to
{stack-ref}/upgrading-elastic-stack.html[Upgrading to Elastic {version}].

.Upgrade from 7.x
IMPORTANT: To upgrade to {version} from 7.16 or an earlier version, **you must
first upgrade to {prev-major-last}**, even if you opt to do a full-cluster
restart instead of a rolling upgrade. This enables you to use the **Upgrade
Assistant** to identify and resolve issues, reindex indices created before 7.0,
and then perform a rolling upgrade. You must resolve all critical issues before
proceeding with the upgrade. For instructions, refer to
{stack-ref}/upgrading-elastic-stack.html#prepare-to-upgrade[Prepare to upgrade
from 7.x].

[discrete]
[[upgrade-index-compatibility]]
=== Index compatibility

{es} can read indices created in the previous major version. If you
have indices created in 6.x or earlier, you must reindex or delete them
before upgrading to {version}. {es} nodes will fail to start if
incompatible indices are present. Snapshots of 6.x or earlier indices cannot be
restored to a 8.x cluster even if they were created by a 7.x cluster. 
The **Upgrade Assistant** in {prev-major-last} identifies any indices 
that need to be reindexed or removed.

[discrete]
[[upgrade-rest-api-compatibility]]
=== REST API compatibility

<<rest-api-compatibility,REST API compatibility>> is a per-request opt-in
feature that can help REST clients mitigate non-compatible (breaking) changes to
the REST API.

[discrete]
[[upgrade-fips-java17]]
=== FIPS Compliance and Java 17

include::{xes-repo-dir}/security/fips-java17.asciidoc[]

include::upgrade/archived-settings.asciidoc[]