Chapter 8. Migrating to KRaft mode If you are using ZooKeeper for metadata management in your Kafka cluster, you can migrate to using Kafka in KRaft mode. KRaft mode replaces ZooKeeper for distributed coordination, offering enhanced reliability, scalability, and throughput. During the migration, you install a quorum of controller nodes as a node pool, which replaces ZooKeeper for management of your cluster. You enable KRaft migration in the cluster configuration by applying the strimzi.io/kraft="migration" annotation. After the migration is complete, you switch the brokers to using KRaft and the controllers out of migration mode using the strimzi.io/kraft="enabled" annotation. Before starting the migration, verify that your environment can support Kafka in KRaft mode, as there are a number of limitations . Note also, the following: Migration is only supported on dedicated controller nodes, not on nodes with dual roles as brokers and controllers. Throughout the migration process, ZooKeeper and controller nodes operate in parallel for a period, requiring sufficient compute resources in the cluster. Prerequisites You must be using Streams for Apache Kafka 2.7 or newer with Kafka 3.7.0 or newer. If you are using an earlier version of Streams for Apache Kafka or Apache Kafka, upgrade before migrating to KRaft mode. Verify that the ZooKeeper-based deployment is operating without the following, as they are not supported in KRaft mode: The Topic Operator running in bidirectional mode. It should either be in unidirectional mode or disabled. JBOD storage. While the jbod storage type can be used, the JBOD array must contain only one disk. The Cluster Operator that manages the Kafka cluster is running. The Kafka cluster deployment uses Kafka node pools. If your ZooKeeper-based cluster is already using node pools, it is ready to migrate. If not, you can migrate the cluster to use node pools . To migrate when the cluster is not using node pools, brokers must be contained in a KafkaNodePool resource configuration that is assigned a broker role and has the name kafka . Support for node pools is enabled in the Kafka resource configuration using the strimzi.io/node-pools: enabled annotation. In this procedure, the Kafka cluster name is my-cluster , which is located in the my-project namespace. The name of the controller node pool created is controller . The node pool for the brokers is called kafka . Procedure For the Kafka cluster, create a node pool with a controller role. The node pool adds a quorum of controller nodes to the cluster. Example configuration for a controller node pool apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaNodePool metadata: name: controller labels: strimzi.io/cluster: my-cluster spec: replicas: 3 roles: - controller storage: type: jbod volumes: - id: 0 type: persistent-claim size: 20Gi deleteClaim: false resources: requests: memory: 64Gi cpu: "8" limits: memory: 64Gi cpu: "12" Note For the migration, you cannot use a node pool of nodes that share the broker and controller roles. Apply the new KafkaNodePool resource to create the controllers. Errors related to using controllers in a ZooKeeper-based environment are expected in the Cluster Operator logs. The errors can block reconciliation. To prevent this, perform the step immediately. Enable KRaft migration in the Kafka resource by setting the strimzi.io/kraft annotation to migration : oc annotate kafka my-cluster strimzi.io/kraft="migration" --overwrite Enabling KRaft migration apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="migration" # ... Applying the annotation to the Kafka resource configuration starts the migration. Check the controllers have started and the brokers have rolled: oc get pods -n my-project Output shows nodes in broker and controller node pools NAME READY STATUS RESTARTS my-cluster-kafka-0 1/1 Running 0 my-cluster-kafka-1 1/1 Running 0 my-cluster-kafka-2 1/1 Running 0 my-cluster-controller-3 1/1 Running 0 my-cluster-controller-4 1/1 Running 0 my-cluster-controller-5 1/1 Running 0 # ... Check the status of the migration: oc get kafka my-cluster -n my-project -w Updates to the metadata state NAME ... METADATA STATE my-cluster ... Zookeeper my-cluster ... KRaftMigration my-cluster ... KRaftDualWriting my-cluster ... KRaftPostMigration METADATA STATE shows the mechanism used to manage Kafka metadata and coordinate operations. At the start of the migration this is ZooKeeper . ZooKeeper is the initial state when metadata is only stored in ZooKeeper. KRaftMigration is the state when the migration is in progress. The flag to enable ZooKeeper to KRaft migration ( zookeeper.metadata.migration.enable ) is added to the brokers and they are rolled to register with the controllers. The migration can take some time at this point depending on the number of topics and partitions in the cluster. KRaftDualWriting is the state when the Kafka cluster is working as a KRaft cluster, but metadata are being stored in both Kafka and ZooKeeper. Brokers are rolled a second time to remove the flag to enable migration. KRaftPostMigration is the state when KRaft mode is enabled for brokers. Metadata are still being stored in both Kafka and ZooKeeper. The migration status is also represented in the status.kafkaMetadataState property of the Kafka resource. Warning You can roll back to using ZooKeeper from this point . The step is to enable KRaft. Rollback cannot be performed after enabling KRaft. When the metadata state has reached KRaftPostMigration , enable KRaft in the Kafka resource configuration by setting the strimzi.io/kraft annotation to enabled : oc annotate kafka my-cluster strimzi.io/kraft="enabled" --overwrite Enabling KRaft migration apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="enabled" # ... Check the status of the move to full KRaft mode: oc get kafka my-cluster -n my-project -w Updates to the metadata state NAME ... METADATA STATE my-cluster ... Zookeeper my-cluster ... KRaftMigration my-cluster ... KRaftDualWriting my-cluster ... KRaftPostMigration my-cluster ... PreKRaft my-cluster ... KRaft PreKRaft is the state when all ZooKeeper-related resources have been automatically deleted. KRaft is the final state (after the controllers have rolled) when the KRaft migration is finalized. Note Depending on how deleteClaim is configured for ZooKeeper, its Persistent Volume Claims (PVCs) and persistent volumes (PVs) may not be deleted. deleteClaim specifies whether the PVC is deleted when the cluster is uninstalled. The default is false . Remove any ZooKeeper-related configuration from the Kafka resource. If present, you can remove the following: log.message.format.version inter.broker.protocol.version spec.zookeeper.* properties Removing log.message.format.version and inter.broker.protocol.version causes the brokers and controllers to roll again. Removing ZooKeeper properties removes any warning messages related to ZooKeeper configuration being present in a KRaft-operated cluster. Performing a rollback on the migration Before the migration is finalized by enabling KRaft in the Kafka resource, and the state has moved to the KRaft state, you can perform a rollback operation as follows: Apply the strimzi.io/kraft="rollback" annotation to the Kafka resource to roll back the brokers. oc annotate kafka my-cluster strimzi.io/kraft="rollback" --overwrite Rolling back KRaft migration apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="rollback" # ... The migration process must be in the KRaftPostMigration state to do this. The brokers are rolled back so that they can be connected to ZooKeeper again and the state returns to KRaftDualWriting . Delete the controllers node pool: oc delete KafkaNodePool controller -n my-project Apply the strimzi.io/kraft="disabled" annotation to the Kafka resource to return the metadata state to ZooKeeper . oc annotate kafka my-cluster strimzi.io/kraft="disabled" --overwrite Switching back to using ZooKeeper apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="disabled" # ...

Commands:
apiVersion: kafka.strimzi.io/v1beta2 kind: KafkaNodePool metadata: name: controller labels: strimzi.io/cluster: my-cluster spec: replicas: 3 roles: - controller storage: type: jbod volumes: - id: 0 type: persistent-claim size: 20Gi deleteClaim: false resources: requests: memory: 64Gi cpu: "8" limits: memory: 64Gi cpu: "12"
annotate kafka my-cluster strimzi.io/kraft="migration" --overwrite
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="migration"
get pods -n my-project
NAME READY STATUS RESTARTS my-cluster-kafka-0 1/1 Running 0 my-cluster-kafka-1 1/1 Running 0 my-cluster-kafka-2 1/1 Running 0 my-cluster-controller-3 1/1 Running 0 my-cluster-controller-4 1/1 Running 0 my-cluster-controller-5 1/1 Running 0
get kafka my-cluster -n my-project -w
NAME ... METADATA STATE my-cluster ... Zookeeper my-cluster ... KRaftMigration my-cluster ... KRaftDualWriting my-cluster ... KRaftPostMigration
annotate kafka my-cluster strimzi.io/kraft="enabled" --overwrite
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="enabled"
get kafka my-cluster -n my-project -w
NAME ... METADATA STATE my-cluster ... Zookeeper my-cluster ... KRaftMigration my-cluster ... KRaftDualWriting my-cluster ... KRaftPostMigration my-cluster ... PreKRaft my-cluster ... KRaft
annotate kafka my-cluster strimzi.io/kraft="rollback" --overwrite
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="rollback"
delete KafkaNodePool controller -n my-project
annotate kafka my-cluster strimzi.io/kraft="disabled" --overwrite
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster namespace: my-project annotations: strimzi.io/kraft="disabled"