Chapter 8. Downgrading AMQ Streams

If you are encountering issues with the version of AMQ Streams you upgraded to, you can revert your installation to the previous version.

You can perform a downgrade to:

  1. Revert your Cluster Operator to the previous AMQ Streams version.

  2. Downgrade all Kafka brokers and client applications to the previous Kafka version.

If the previous version of AMQ Streams does not support the version of Kafka you are using, you can also downgrade Kafka as long as the log message format versions appended to messages match.

8.1. Downgrading the Cluster Operator to a previous version

If you are encountering issues with AMQ Streams, you can revert your installation.

This procedure describes how to downgrade a Cluster Operator deployment to a previous version.

Prerequisites

Procedure

  1. 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 previous version of the Cluster Operator.
  2. Revert your custom resources to reflect the supported configuration options available for the version of AMQ Streams you are downgrading to.

  3. Update the Cluster Operator.

    1. Modify the installation files for the previous version according to the namespace the Cluster Operator is running in.

      On Linux, use: 

      sed -i 's/namespace: .*/namespace: my-cluster-operator-namespace/' install/cluster-operator/*RoleBinding*.yaml

      On MacOS, use: 

      sed -i '' 's/namespace: .*/namespace: my-cluster-operator-namespace/' install/cluster-operator/*RoleBinding*.yaml
    2. 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.

  4. When you have an updated configuration, deploy it along with the rest of the installation resources: 

    oc apply -f install/cluster-operator

    Wait for the rolling updates to complete.

  5. 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 AMQ Streams version followed by the Kafka version. For example, NEW-STREAMS-VERSION-kafka-CURRENT-KAFKA-VERSION.

Your Cluster Operator was downgraded to the previous version.

8.2. Downgrading Kafka

Kafka version downgrades are performed by the Cluster Operator.

8.2.1. 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 previous 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 previous version, including when the default value for log.message.format.version is used. For example, this resource can be downgraded to Kafka version 2.5.0 because the log.message.format.version has not been changed: 

apiVersion: kafka.strimzi.io/v1beta1
kind: Kafka
spec:
  # ...
  kafka:
    version: 2.6.0
    config:
      log.message.format.version: "2.5"
      # ...

The downgrade would not be possible if the log.message.format.version was set at "2.6" or a value was absent (so that the parameter took the default value for a 2.6.0 broker of 2.6).

8.2.2. Downgrading Kafka brokers and client applications

This procedure describes how you can downgrade a AMQ Streams Kafka cluster to a lower (previous) version of Kafka, such as downgrading from 2.6.0 to 2.5.0.

Prerequisites

For the Kafka resource to be downgraded, check:

  • IMPORTANT: Compatibility of Kafka versions.
  • The Cluster Operator, which supports both versions of Kafka, is up and running.
  • The Kafka.spec.kafka.config does not contain options that are not supported by the Kafka version being downgraded to.
  • The 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.

Procedure

  1. Update the Kafka cluster configuration in an editor, as required. 

    oc edit kafka my-cluster

  2. Change the Kafka.spec.kafka.version to specify the previous version.

    For example, if downgrading from Kafka 2.6.0 to 2.5.0: 

    apiVersion: kafka.strimzi.io/v1beta1
kind: Kafka
spec:
  # ...
  kafka:
    version: 2.5.0 1
    config:
      log.message.format.version: "2.5" 2
      inter.broker.protocol.version: "2.5" 3
      # ...
    1
    Kafka version is changed to the previous version.
    2
    Message format version is unchanged.
    3
    Inter-broker protocol version is unchanged.
    Note

    You must format the value of log.message.format.version and inter.broker.protocol.version as a string to prevent it from being interpreted as a floating point number.

  3. 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 7.1.3.1, “Kafka version and image mappings”

  4. Save and exit the editor, then wait for rolling updates to complete.

    Check the update in the logs or by watching the pod state transitions: 

    oc logs -f CLUSTER-OPERATOR-POD-NAME | grep -E "Kafka version downgrade from [0-9.]+ to [0-9.]+, phase ([0-9]+) of \1 completed"
    oc get pod -w

    Check the Cluster Operator logs for an INFO level message: 

    Reconciliation #NUM(watch) Kafka(NAMESPACE/NAME): Kafka version downgrade from FROM-VERSION to TO-VERSION, phase 1 of 1 completed

  5. Downgrade all client applications (consumers) to use the previous version of the client binaries.

    The Kafka cluster and clients are now using the previous Kafka version.