Chapter 26. Downgrading Streams for Apache Kafka If you are encountering issues with the version of Streams for Apache Kafka you upgraded to, you can revert your installation to the version. If you used the YAML installation files to install Streams for Apache Kafka, you can use the YAML installation files from the release to perform the downgrade procedures. You can downgrade Streams for Apache Kafka by updating the Cluster Operator and the version of Kafka you are using. Kafka version downgrades are performed by the Cluster Operator. Warning The following downgrade instructions are only suitable if you installed Streams for Apache Kafka using the installation files. If you installed Streams for Apache Kafka using another method, like OperatorHub, downgrade may not be supported by that method unless specified in their documentation. To ensure a successful downgrade process, it is essential to use a supported approach. 26.1. Downgrading the Cluster Operator to a version If you are encountering issues with Streams for Apache Kafka, you can revert your installation. This procedure describes how to downgrade a Cluster Operator deployment to a version. Prerequisites An existing Cluster Operator deployment is available. You have downloaded the installation files for the version . Before you begin Check the downgrade requirements of the Streams for Apache Kafka feature gates . If a feature gate is permanently enabled, you may need to downgrade to a version that allows you to disable it before downgrading to your target version. Procedure Take note of any configuration changes made to the existing Cluster Operator resources (in the /install/cluster-operator directory). Any changes will be overwritten by the version of the Cluster Operator. Revert your custom resources to reflect the supported configuration options available for the version of Streams for Apache Kafka you are downgrading to. Update the Cluster Operator. Modify the installation files for the version according to the namespace the Cluster Operator is running in. On Linux, use: On MacOS, use: If you modified one or more environment variables in your existing Cluster Operator Deployment , edit the install/cluster-operator/060-Deployment-strimzi-cluster-operator.yaml file to use those environment variables. When you have an updated configuration, deploy it along with the rest of the installation resources: oc replace -f install/cluster-operator Wait for the rolling updates to complete. Get the image for the Kafka pod to ensure the downgrade was successful: oc get pod my-cluster-kafka-0 -o jsonpath='{.spec.containers[0].image}' The image tag shows the new Streams for Apache Kafka version followed by the Kafka version. For example, <strimzi_version>-kafka-<kafka_version> . You can also check the downgrade has completed successfully from the status of the Kafka resource . 26.2. Downgrading KRaft-based Kafka clusters and client applications Downgrade a KRaft-based Streams for Apache Kafka cluster to an earlier version. When downgrading a KRaft-based Streams for Apache Kafka cluster to a lower version, like moving from 3.7.0 to 3.6.0, ensure that the metadata version used by the Kafka cluster is a version supported by the Kafka version you want to downgrade to. The metadata version for the Kafka version you are downgrading from must not be higher than the version you are downgrading to. Note Consult the Apache Kafka documentation for information regarding the support and limitations associated with KRaft-based downgrades. Prerequisites The Cluster Operator is up and running. Before you downgrade the Streams for Apache Kafka cluster, check the following for the Kafka resource: The Kafka custom resource does not contain options that are not supported by the Kafka version being downgraded to. spec.kafka.metadataVersion is set to a version that is supported by the Kafka version being downgraded to. Procedure Update the Kafka cluster configuration. oc edit kafka <kafka_configuration_file> Change the metadataVersion version to a version supported by the Kafka version you are downgrading to; leave the Kafka.spec.kafka.version unchanged at the current Kafka version. For example, if downgrading from Kafka 3.7.0 to 3.6.0: apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: kafka: replicas: 3 metadataVersion: 3.6-IV2 1 version: 3.7.0 2 # ... 1 Metadata version is changed to a version supported by the earlier Kafka version. 2 Kafka version is unchanged. Note The value of metadataVersion must be a string to prevent it from being interpreted as a floating point number. Save the change, and wait for Cluster Operator to update .status.kafkaMetadataVersion for the Kafka resource. Change the Kafka.spec.kafka.version to the version. For example, if downgrading from Kafka 3.7.0 to 3.6.0: apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: kafka: replicas: 3 metadataVersion: 3.6-IV2 1 version: 3.6.0 2 # ... 1 Metadata version is supported by the Kafka version. 2 Kafka version is changed to the new version. If the image for the Kafka version is different from the image defined in STRIMZI_KAFKA_IMAGES for the Cluster Operator, update Kafka.spec.kafka.image . See Section 25.2.3, "Kafka version and image mappings" . Wait for the Cluster Operator to update the cluster. You can check the downgrade has completed successfully from the status of the Kafka resource . Downgrade all client applications (consumers) to use the version of the client binaries. The Kafka cluster and clients are now using the Kafka version. 26.3. Downgrading Kafka when using ZooKeeper If you are using Kafka in ZooKeeper mode, the downgrade process involves changing the Kafka version and the related log.message.format.version and inter.broker.protocol.version properties. 26.3.1. Kafka version compatibility for downgrades Kafka downgrades are dependent on compatible current and target Kafka versions , and the state at which messages have been logged. You cannot revert to the Kafka version if that version does not support any of the inter.broker.protocol.version settings which have ever been used in that cluster, or messages have been added to message logs that use a newer log.message.format.version . The inter.broker.protocol.version determines the schemas used for persistent metadata stored by the broker, such as the schema for messages written to __consumer_offsets . If you downgrade to a version of Kafka that does not understand an inter.broker.protocol.version that has ever been previously used in the cluster the broker will encounter data it cannot understand. If the target downgrade version of Kafka has: The same log.message.format.version as the current version, the Cluster Operator downgrades by performing a single rolling restart of the brokers. A different log.message.format.version , downgrading is only possible if the running cluster has always had log.message.format.version set to the version used by the downgraded version. This is typically only the case if the upgrade procedure was aborted before the log.message.format.version was changed. In this case, the downgrade requires: Two rolling restarts of the brokers if the interbroker protocol of the two versions is different A single rolling restart if they are the same Downgrading is not possible if the new version has ever used a log.message.format.version that is not supported by the version, including when the default value for log.message.format.version is used. For example, this resource can be downgraded to Kafka version 3.6.0 because the log.message.format.version has not been changed: apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka spec: # ... kafka: version: 3.7.0 config: log.message.format.version: "3.6" # ... The downgrade would not be possible if the log.message.format.version was set at "3.7" or a value was absent, so that the parameter took the default value for a 3.7.0 broker of 3.7. Important From Kafka 3.0.0, when the inter.broker.protocol.version is set to 3.0 or higher, the log.message.format.version option is ignored and doesn't need to be set. 26.3.2. Downgrading ZooKeeper-based Kafka clusters and client applications Downgrade a ZooKeeper-based Streams for Apache Kafka cluster to an earlier version. When downgrading a ZooKeeper-based Streams for Apache Kafka cluster to a lower version, like moving from 3.7.0 to 3.6.0, ensure that the inter-broker protocol version used by the Kafka cluster is a version supported by the Kafka version you want to downgrade to. The inter-broker protocol version for the Kafka version you are downgrading from must not be higher than the version you are downgrading to. Note Consult the Apache Kafka documentation for information regarding the support and limitations associated with ZooKeeper-based downgrades. Prerequisites The Cluster Operator is up and running. Before you downgrade the Streams for Apache Kafka cluster, check the following for the Kafka resource: IMPORTANT: Compatibility of Kafka versions . The Kafka custom resource does not contain options that are not supported by the Kafka version being downgraded to. Kafka.spec.kafka.config has a log.message.format.version and inter.broker.protocol.version that is supported by the Kafka version being downgraded to. From Kafka 3.0.0, when the inter.broker.protocol.version is set to 3.0 or higher, the log.message.format.version option is ignored and doesn't need to be set. Procedure Update the Kafka cluster configuration. oc edit kafka <kafka_configuration_file> Change the inter.broker.protocol.version version (and log.message.format.version , if applicable) to a version supported by the Kafka version you are downgrading to; leave the Kafka.spec.kafka.version unchanged at the current Kafka version. For example, if downgrading from Kafka 3.7.0 to 3.6.0: apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: # ... kafka: version: 3.7.0 1 config: inter.broker.protocol.version: "3.6" 2 log.message.format.version: "3.6" # ... 1 Kafka version is unchanged. 2 Inter-broker protocol version is changed to a version supported by the earlier Kafka version. Note The value of log.message.format.version and inter.broker.protocol.version must be strings to prevent them from being interpreted as floating point numbers. Save and exit the editor, then wait for rolling updates to complete. Check the progress of the rolling updates by watching the pod state transitions: oc get pods my-cluster-kafka-0 -o jsonpath='{.spec.containers[0].image}' The rolling updates ensure that each pod is using the specified Kafka inter-broker protocol version. Change the Kafka.spec.kafka.version to the version. For example, if downgrading from Kafka 3.7.0 to 3.6.0: apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: # ... kafka: version: 3.6.0 1 config: inter.broker.protocol.version: "3.6" 2 log.message.format.version: "3.6" # ... 1 Kafka version is changed to the new version. 2 Inter-broker protocol version is supported by the Kafka version. If the image for the Kafka version is different from the image defined in STRIMZI_KAFKA_IMAGES for the Cluster Operator, update Kafka.spec.kafka.image . See Section 25.2.3, "Kafka version and image mappings" . Wait for the Cluster Operator to update the cluster. You can check the downgrade has completed successfully from the status of the Kafka resource . Downgrade all client applications (consumers) to use the version of the client binaries. The Kafka cluster and clients are now using the Kafka version. If you are reverting back to a version of Streams for Apache Kafka earlier than 1.7, which uses ZooKeeper for the storage of topic metadata, delete the internal topic store topics from the Kafka cluster. oc run kafka-admin -ti --image=registry.redhat.io/amq-streams/kafka-37-rhel9:2.7.0 --rm=true --restart=Never -- ./bin/kafka-topics.sh --bootstrap-server localhost:9092 --topic __strimzi-topic-operator-kstreams-topic-store-changelog --delete && ./bin/kafka-topics.sh --bootstrap-server localhost:9092 --topic __strimzi_store_topic --delete

Commands:
sed -i 's/namespace: .*/namespace: my-cluster-operator-namespace/' install/cluster-operator/*RoleBinding*.yaml
sed -i '' 's/namespace: .*/namespace: my-cluster-operator-namespace/' install/cluster-operator/*RoleBinding*.yaml
replace -f install/cluster-operator
get pod my-cluster-kafka-0 -o jsonpath='{.spec.containers[0].image}'
edit kafka <kafka_configuration_file>
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: kafka: replicas: 3 metadataVersion: 3.6-IV2 1 version: 3.7.0 2 #
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: kafka: replicas: 3 metadataVersion: 3.6-IV2 1 version: 3.6.0 2 #
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka spec: # kafka: version: 3.7.0 config: log.message.format.version: "3.6" #
edit kafka <kafka_configuration_file>
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: # kafka: version: 3.7.0 1 config: inter.broker.protocol.version: "3.6" 2 log.message.format.version: "3.6" #
get pods my-cluster-kafka-0 -o jsonpath='{.spec.containers[0].image}'
apiVersion: kafka.strimzi.io/v1beta2 kind: Kafka metadata: name: my-cluster spec: # kafka: version: 3.6.0 1 config: inter.broker.protocol.version: "3.6" 2 log.message.format.version: "3.6" #
run kafka-admin -ti --image=registry.redhat.io/amq-streams/kafka-37-rhel9:2.7.0 --rm=true --restart=Never -- ./bin/kafka-topics.sh --bootstrap-server localhost:9092 --topic __strimzi-topic-operator-kstreams-topic-store-changelog --delete && ./bin/kafka-topics.sh --bootstrap-server localhost:9092 --topic __strimzi_store_topic --delete