Note: All commands are written for juju >= v.3.0
If you are using an earlier version, check the Juju 3.0 Release Notes.
How to perform a minor rollback
Example: PostgreSQL 14.9 → PostgreSQL 14.8
(including simple charm revision bump: from revision 43 to revision 42)
After a juju refresh, if there are any version incompatibilities in charm revisions, its dependencies, or any other unexpected failure in the upgrade process, the process will be halted and enter a failure state.
Even if the underlying PostgreSQL cluster continues to work, it’s important to roll back the charm to a previous revision so that an update can be attempted after further inspection of the failure.
Warning: Do NOT trigger rollback during the running upgrade action! It may cause an unpredictable PostgreSQL cluster state!
Summary
- Prepare the Charmed PostgreSQL K8s application for the in-place rollback.
- Rollback. Perform the first charm rollback - only the first unit. The unit with the maximal ordinal will be chosen.
- Resume. Continue rollback to all other units if the first unit rolled back successfully.
- Check. Make sure the charm and cluster are in healthy state again.
Step 1: Prepare
To execute a rollback, we use a similar procedure to the upgrade. The difference is the charm revision to upgrade to. In this guide’s example, we will refresh the charm back to revision 88.
It is necessary to re-run pre-upgrade-check action on the leader unit to enter the upgrade recovery state:
juju run postgresql-k8s/leader pre-upgrade-check
Step 2: Rollback
When using a charm from charmhub:
juju refresh postgresql-k8s --revision=88
When deploying from a local charm file, one must have the previous revision charm file and the postgresql-image resource, then run
juju refresh postgresql-k8s --path=./postgresql-k8s_ubuntu-22.04-amd64.charm \
--resource postgresql-image=ghcr.io/canonical/charmed-postgresql:797a2132
…where postgresql-k8s_ubuntu-22.04-amd64.charm is the previous revision charm file. The reference for the resource for a given revision can be found at the metadata.yaml file in the charm repository.
The first unit will be rolled out and should rejoin the cluster after settling down. After the refresh command, the juju controller revision for the application will be back in sync with the running Charmed PostgreSQL K8s revision.
Step 3: Resume
We still need to resume the upgrade on the remaining units, which is done with the resume-upgrade action.
juju run postgresql-k8s/leader resume-upgrade
This will roll out the pods in the remaining units, but to the same charm revision.
Step 4: Check
Future improvements are planned to check the state on pods/clusters on a low level. At the moment, check juju status to make sure the cluster state is OK.