Migration from Zookeper to Apache Kafka Raft (KRaft) for Kafka online

KRaft replaces Zookeeper. Kafka pods become brokers, and Zookeeper pods become controllers. Kafka runs on dual-mode during the migration.

Prerequisites

To bootstrap from a live cluster, complete the following steps:

Make sure that all the operator and datastore pods are running before you begin the migration.

kubectl get all -n instana-kafka

Migration Steps

You must enable node-pool to support both broker and controller.

kubectl annotate kafka instana -n instana-kafka strimzi.io/node-pools="enabled" --overwrite

Disable KRaft.

kubectl annotate kafka instana -n instana-kafka strimzi.io/kraft="disabled" --overwrite

Create a YAML file for the broker. For example, kafka-broker.yaml with the broker configuration.

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaNodePool
metadata:
  name: kafka
  labels:
    strimzi.io/cluster: instana
spec:
  replicas: 3
  roles:
     - broker
  storage:
    type: jbod
    volumes:
      - id: 0
        type: persistent-claim
        size: 50Gi
        deleteClaim: true
  template:
    pod:
      tmpDirSizeLimit: 500Mi

Deploy Broker.

kubectl apply -f kafka-broker.yaml -n instana-kafka

Broker pods appear.

Create a YAML file for the controller. For example, kafka-controller.yaml with the controller configuration.

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaNodePool
metadata:
  name: controller
  labels:
    strimzi.io/cluster: instana
spec:
  replicas: 3
  roles:
    - controller
  storage:
    type: persistent-claim
    size: 50Gi
    deleteClaim: true
  template:
    pod:
      tmpDirSizeLimit: 500Mi

Deploy Controller.

kubectl apply -f kafka-controller.yaml -n instana-kafka

You can use this command to verify the state of node pools.

kubectl get kafka kafka -n instana-kafka -o jsonpath='{.status.kafkaNodePools}'

Enable migration.
```
kubectl annotate kafka instana -n instana-kafka strimzi.io/kraft="migration" --overwrite
```
Controller pods appear, and broker pods restart to connect with the controller.

Verify the migration status.

kubectl get kafka instana -n instana-kafka -o jsonpath='{.status.kafkaMetadataState}'

Replica and storage fields in the kafka.yaml are ignored now. You can remove these fields from the file.

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
metadata:
  ...
  spec:
     kafka:
       ...
       #  replicas: 3
       ...
     #    storage:
     #      type: jbod
     #      volumes:
     #        - id: 0
     #          type: persistent-claim
     #          size: 50Gi
     #          deleteClaim: true
     #  zookeeper:
     #    replicas: 3
     #    storage:
     #      type: persistent-claim
     #      size: 5Gi
     #      deleteClaim: true
     ...

Set the KRaft status to enable when the state is 'KRaftPostMigration'.

kubectl annotate kafka instana -n instana-kafka strimzi.io/kraft="enabled" --overwrite

Broker and controller pods are restarted. Kafka and Zookeeper pods are terminated.

Verify the migration status again.

kubectl get kafka instana -n instana-kafka -o jsonpath='{.status.kafkaMetadataState}'

The state must show KRaft now.

Verify the deployment.

kubectl get all -n instana-kafka

The output might be as the following example.

NAME                                           READY   STATUS    RESTARTS   AGE
pod/instana-entity-operator-8564975588-mrz2f   3/3     Running   0          15m
pod/instana-kafka-0                            1/1     Running   0          16m
pod/instana-kafka-1                            1/1     Running   0          16m
pod/instana-kafka-2                            1/1     Running   0          16m
pod/instana-controller-0                       1/1     Running   0          17m
pod/instana-controller-1                       1/1     Running   0          17m
pod/instana-controller-2                       1/1     Running   0          17m
pod/strimzi-cluster-operator-cf49c75d8-qm8jq   1/1     Running   0          34m

NAME                               TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)                      AGE
service/instana-kafka-bootstrap    ClusterIP   192.168.1.239   <none>        9091/TCP,9092/TCP            16m
service/instana-kafka-brokers      ClusterIP   None            <none>        9090/TCP,9091/TCP,9092/TCP   16m

NAME                                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/instana-entity-operator    1/1     1            1           15m
deployment.apps/strimzi-cluster-operator   1/1     1            1           34m

NAME                                                 DESIRED   CURRENT   READY   AGE
replicaset.apps/instana-entity-operator-8564975588   1         1         1       15m
replicaset.apps/strimzi-cluster-operator-cf49c75d8   1         1         1       34m