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<@tmpl.guide
title="Avoiding downtime with rolling updates"
summary="Avoid downtimes when changing themes, providers or configurations in optimized images.">

By default, the {project_name} Operator will perform rolling updates on configuration changes without downtime, and recreate updates with downtime when the image name or tag changes.

This {section} describes how to minimize downtimes by configuring the {project_name} Operator to perform rolling updates of {project_name} automatically where possible, and how to override automatic detection for rolling updates.

Use it, for example, to avoid downtimes when rolling out an update to a theme, provider or build time configuration in a custom or optimized image.

== Supported Update Strategies

The Operator supports the following update strategies:

Rolling Updates:: Update the StatefulSet in a rolling fashion, avoiding a downtime when at least two replicas are running.

Recreate Updates:: Scale down the StatefulSet before applying updates, causing temporary downtime.

== Configuring the Update Strategy

Specify the update strategy within the `spec` section of the Keycloak CR YAML definition:

[source,yaml]
----
apiVersion: k8s.keycloak.org/v2alpha1
kind: Keycloak
metadata:
  name: example-kc
spec:
  update:
    strategy: RecreateOnImageChange|Auto|Explicit # <1>
    revision: "abc" # <2>
----
<.> Set the desired update strategy here.
<.> Revision value for `Explicit` strategy.
Ignored by the other strategies.

[%autowidth]
.Possible field values
|===
|Value |Downtime? |Description

|`RecreateOnImageChange` (default)
|On image name or tag change
|Mimics {project_name} 26.1 or older behavior.
When the image field changes, the Operator scales down the StatefulSet before applying the new image.

|`Auto`
|On incompatible changes
|The {project_name} Operator detects if a rolling or recreate update is possible.

In the current version, {project_name} performs rolling update if the {project_name} version is the same for the old and the new image.
Future versions of {project_name} will change that behavior and use additional information from the configuration, the image and the version to determine if a rolling update is possible to reduce downtimes.

|`Explicit`
|Only the `revision` field changes
|The {project_name} Operator checks the `spec.update.revision` value.
If it matches the previous deployment, it performs a rolling update.

|===

=== Understanding `Auto` and `Explicit` Update Strategies

When using the `Auto` update strategy, the {project_name} Operator automatically starts a Job to assess the feasibility of a rolling update.
Read more about the process in the <@links.server id="update-compatibility"/> {section}.
This process consumes cluster resources for the time of the check and introduces a slight delay before the StatefulSet update begins.

The `Explicit` update strategy delegates the update decision to the user.
The `revision` field acts as a user-controlled trigger.
While the {project_name} Operator does not interpret the `revision` value itself, any change to the Custom Resource (CR) while the `revision` remains unchanged will prompt a rolling update.

Exercise caution when using this with automatic Operator upgrades.
The Operator Lifecycle Manager (OLM) may upgrade the {project_name} Operator, and if the `Explicit` update strategy is in use, this could lead to unexpected behavior or deployment failures as the Operator would attempt a rolling update when this is actually not supported.
**If you are using the `Explicit` update strategy, thorough testing in a non-production environment is highly recommended before upgrading.**

=== CR Statuses

The Keycloak CR status of `RecreateUpdateUsed` indicates the update strategy employed during the last update operation.
The `lastTransitionTime` field indicates when the last update occurred.
Use this information to observe actions and decisions taken by the Operator.

[%autowidth]
.Condition statuses
|===
|Status |Description

m|Unknown
|The initial state.
It means no update has taken place.

m|False
|The Operator applied the rolling update strategy in the last update.

m|True
|The Operator applied the recreate update strategy in the last update.
The `message` field explains why this strategy was chosen.

|===

</@tmpl.guide>

