MySQL Router K8s How-to - Minor rollback

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Minor Rollback

:information_source: Example: MySQL Router 8.0.34 → MySQL Router 8.0.33
(including simple charm revision bump: from revision 43 to revision 42)

:warning: WARNING: do NOT trigger rollback during the running upgrade action! It may cause unpredictable MySQL Cluster and/or MySQL Router state!

Minor rollback steps

  1. Rollback. Perform the charm rollback using juju refresh. The unit with the maximal ordinal will be rolled back first, and the rollback will continue for the entire application.
  2. Check. Make sure the charm and cluster are in healthy state again.

Manual Rollback

After a juju refresh, case there any version incompatibilities in charm revisions or it dependencies, or any other unexpected failure in the upgrade process, the upgrade process will be halted an enter a failure state.

Although the underlying MySQL Cluster and MySQL Router continue to work, it’s important to rollback the charm to previous revision so an update can be later attempted after a further inspection of the failure.

To execute a rollback we take the same procedure as the upgrade, the difference being the charm revision to upgrade to. In case of this tutorial example, one would refresh the charm back to revision 88, the steps being:

Step 1: Rollback

When using the charm from charmhub:

juju refresh mysql-router-k8s --revision=88 --trust

When deploying from a local charm file, you need to have the previous revision’s .charm file and the mysql-image resource. Then, run:

juju refresh mysql-router-k8s --trust --path=<path_to_charm_file> \
       --resource mysql-router-image=<image>

The resource reference can be found under the upstream-source key in the charm’s metadata.yaml file. You can access this file by:

  • Simply unpacking the .charm file
  • Finding the corresponding release in the charm’s GitHub repository and navigating to metadata.yaml.

After the refresh command, the juju controller revision for the application will be back in sync with the running MySQL Router K8s revision.

Step 2: Check

Future improvement are planned to check the state on pod/cluster on a low level.

For now, use juju status to check the cluster state.