// Module included in the following assemblies:
//
// assembly-using-the-cluster-operator.adoc

[id='ref-operator-cluster-feature-gates-{context}']
= Configuring feature gates

[role="_abstract"]
Strimzi operators support _feature gates_ to enable or disable certain features and functionality.
Enabling a feature gate changes the behavior of the relevant operator and introduces the feature to your Strimzi deployment.

Feature gates have a default state of either _enabled_ or _disabled_.

To modify a feature gate's default state, use the `STRIMZI_FEATURE_GATES` environment variable in the operator's configuration.
You can modify multiple feature gates using this single environment variable.
Specify a comma-separated list of feature gate names and prefixes.
A `+` prefix enables the feature gate and a `-` prefix  disables it.

.Example feature gate configuration that enables `FeatureGate1` and disables `FeatureGate2`
[source,yaml,options="nowrap"]
----
env:
  - name: STRIMZI_FEATURE_GATES
    value: +FeatureGate1,-FeatureGate2
----

== ControlPlaneListener feature gate

The `ControlPlaneListener` feature gate has moved to GA, which means it is now permanently enabled and cannot be disabled.
With `ControlPlaneListener` enabled, the connections between the Kafka controller and brokers use an internal _control plane listener_ on port 9090.
Replication of data between brokers, as well as internal connections from Strimzi operators, Cruise Control, or the Kafka Exporter use the _replication listener_ on port 9091.

IMPORTANT: With the `ControlPlaneListener` feature gate permanently enabled, it is no longer possible to upgrade or downgrade directly between Strimzi 0.22 and earlier and Strimzi 0.32 and newer.
You have to first upgrade or downgrade through one of the Strimzi versions in-between, disable the `ControlPlaneListener` feature gate, and then downgrade or upgrade (with the feature gate enabled) to the target version.

== ServiceAccountPatching feature gate

The `ServiceAccountPatching` feature gate has moved to GA, which means it is now permanently enabled and cannot be disabled.
With `ServiceAccountPatching` enabled, the Cluster Operator always reconciles service accounts and updates them when needed.
For example, when you change service account labels or annotations using the `template` property of a custom resource, the operator automatically updates them on the existing service account resources.

[id='ref-operator-use-strimzi-pod-sets-feature-gate-{context}']
== UseStrimziPodSets feature gate

The `UseStrimziPodSets` feature gate has moved to GA, which means it is now permanently enabled and cannot be disabled.
Support for `StatefulSets` has been removed and Strimzi is now always using `StrimziPodSets` to manage Kafka and ZooKeeper pods.

IMPORTANT: With the `UseStrimziPodSets` feature gate permanently enabled, it is no longer possible to downgrade directly from Strimzi 0.35 and newer to Strimzi 0.27 or earlier.
You have to first downgrade through one of the Strimzi versions in-between, disable the `UseStrimziPodSets` feature gate, and then downgrade to Strimzi 0.27 or earlier.

[id='ref-operator-use-kraft-feature-gate-{context}']
== (Preview) UseKRaft feature gate

The `UseKRaft` feature gate has a default state of _disabled_.

The `UseKRaft` feature gate deploys the Kafka cluster in the KRaft (Kafka Raft metadata) mode without ZooKeeper.
ZooKeeper and KRaft are mechanisms used to manage metadata and coordinate operations in Kafka clusters. 
KRaft mode eliminates the need for an external coordination service like ZooKeeper. 
In KRaft mode, Kafka nodes take on the roles of brokers, controllers, or both. 
They collectively manage the metadata, which is replicated across partitions. 
Controllers are responsible for coordinating operations and maintaining the cluster's state.

This feature gate is currently intended only for development and testing.

IMPORTANT: **KRaft mode is not ready for production in Apache Kafka or in Strimzi.**

Enabling the `UseKRaft` feature gate requires the `KafkaNodePools` feature gate to be enabled as well.
To deploy a Kafka cluster in KRaft mode, you must use the `KafkaNodePool` resources.
For more details and examples, see xref:deploying-kafka-node-pools-{context}[].

When the `UseKRaft` feature gate is enabled, the Kafka cluster is deployed without ZooKeeper.
*The `.spec.zookeeper` properties in the `Kafka` custom resource are ignored, but still need to be present.*
The `UseKRaft` feature gate provides an API that configures Kafka cluster nodes and their roles.
The API is still in development and is expected to change before the KRaft mode is production-ready.

Currently, the KRaft mode in Strimzi has the following major limitations:

* Moving from Kafka clusters with ZooKeeper to KRaft clusters or the other way around is not supported.
* Controller-only nodes cannot undergo rolling updates or be updated individually.
* Upgrades and downgrades of Apache Kafka versions or the Strimzi operator are not supported.
  Users might need to delete the cluster, upgrade the operator and deploy a new Kafka cluster.
* Only the _Unidirectional_ Topic Operator is supported in KRaft mode.
  You can enable it using the `UnidirectionalTopicOperator` feature gate.
  The _Bidirectional_ Topic Operator is not supported and when the `UnidirectionalTopicOperator` feature gate is not enabled, the `spec.entityOperator.topicOperator` property *must be removed* from the `Kafka` custom resource.
* JBOD storage is not supported. 
  The `type: jbod` storage can be used, but the JBOD array can contain only one disk.

.Enabling the UseKRaft feature gate
To enable the `UseKRaft` feature gate, specify `+UseKRaft,+KafkaNodePools` in the `STRIMZI_FEATURE_GATES` environment variable in the Cluster Operator configuration.

[id='ref-operator-stable-connect-identities-feature-gate-{context}']
== StableConnectIdentities feature gate

The `StableConnectIdentities` feature gate has a default state of _disabled_.

The `StableConnectIdentities` feature gate uses `StrimziPodSet` resources to manage Kafka Connect and Kafka MirrorMaker 2 pods instead of using Kubernetes `Deployment` resources.
`StrimziPodSets` give the pods stable names and stable addresses, which do not change during rolling upgrades.
This helps to minimize the number of rebalances of connector tasks.

.Enabling the `StableConnectIdentities` feature gate
To enable the `StableConnectIdentities` feature gate, specify `+StableConnectIdentities` in the `STRIMZI_FEATURE_GATES` environment variable in the Cluster Operator configuration.

IMPORTANT: The `StableConnectIdentities` feature gate must be disabled when downgrading to Strimzi 0.33 and earlier versions.

[id='ref-operator-kafka-node-pools-feature-gate-{context}']
== (Preview) KafkaNodePools feature gate

The `KafkaNodePools` feature gate has a default state of _disabled_.

The `KafkaNodePools` feature gate introduces a new `KafkaNodePool` custom resource that enables the configuration of different _pools_ of Apache Kafka nodes.

A node pool refers to a distinct group of Kafka nodes within a Kafka cluster.
Each pool has its own unique configuration, which includes mandatory settings such as the number of replicas, storage configuration, and a list of assigned roles.
You can assign the _controller_ role, _broker_ role, or both roles to all nodes in the pool in the `.spec.roles` field.
When used with a ZooKeeper-based Apache Kafka cluster, it must be set to the `broker` role.
When used with the `UseKRaft` feature gate, it can be set to `broker`, `controller`, or both.

In addition, a node pool can have its own configuration of resource requests and limits, Java JVM options, and resource templates.
Configuration options not set in the `KafkaNodePool` resource are inherited from the `Kafka` custom resource.

The `KafkaNodePool` resources use a `strimzi.io/cluster` label to indicate to which Kafka cluster they belong.
The label must be set to the name of the `Kafka` custom resource.

Examples of the `KafkaNodePool` resources can be found in the xref:config-examples-{context}[example configuration files] provided by Strimzi.

.Enabling the KafkaNodePools feature gate

To enable the `KafkaNodePools` feature gate, specify `+KafkaNodePools` in the `STRIMZI_FEATURE_GATES` environment variable in the Cluster Operator configuration.
The `Kafka` custom resource using the node pools must also have the annotation `strimzi.io/node-pools: enabled`.

[id='ref-operator-unidirectional-topic-operator-feature-gate-{context}']
== (Preview) UnidirectionalTopicOperator feature gate

The `UnidirectionalTopicOperator` feature gate has a default state of _disabled_.

The `UnidirectionalTopicOperator` feature gate introduces a unidirectional topic management mode for creating Kafka topics using the `KafkaTopic` resource.
Unidirectional mode is compatible with using KRaft for cluster management.
With unidirectional mode, you create Kafka topics using the `KafkaTopic` resource, which are then managed by the Topic Operator.
Any configuration changes to a topic outside the `KafkaTopic` resource are reverted.
For more information on topic management, see xref:ref-operator-topic-str[].

.Enabling the UnidirectionalTopicOperator feature gate

To enable the `UnidirectionalTopicOperator` feature gate, specify `+UnidirectionalTopicOperator` in the `STRIMZI_FEATURE_GATES` environment variable in the Cluster Operator configuration.
For the `KafkaTopic` custom resource to use this feature, the `strimzi.io/managed` annotation is set to `true` by default. 