Charmed PostgreSQL VM

Channel Revision Published Runs on
latest/stable 345 09 Nov 2023
Ubuntu 22.04 Ubuntu 20.04 Ubuntu 18.04 Ubuntu 16.04
14/stable 363 21 Feb 2024
Ubuntu 22.04
14/candidate 405 03 May 2024
Ubuntu 22.04
14/beta 409 23 May 2024
Ubuntu 22.04
14/edge 409 21 May 2024
Ubuntu 22.04
juju deploy postgresql --channel 14/stable
Show information

Platform:

Ubuntu
22.04

Minor Rollback

Example: PostgreSQL 14.9 → PostgreSQL 14.8
(including simple charm revision bump: from revision 43 to revision 42)

Warning: Do NOT trigger rollback during the running upgrade action! It may cause an unpredictable PostgreSQL cluster state!

Note: All commands are written for juju >= v.3.0

If you are using an earlier version, be aware that:

  • juju run replaces juju run-action --wait in juju v.2.9
  • juju integrate replaces juju relate and juju add-relation in juju v.2.9

For more information, check the Juju 3.0 Release Notes.

Manual rollback

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.

Minor rollback steps

  1. Prepare the Charmed PostgreSQL VM application for the in-place rollback.
  2. Rollback. Once started, all units in a cluster will be executed sequentially. The rollback will be aborted (paused) if the unit rollback has failed.
  3. Check. Make sure the charm and cluster are in a healthy state again.

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 182.

Step 1: Prepare

It is necessary to re-run pre-upgrade-check action on the leader unit, to enter the upgrade recovery state:

juju run postgresql/leader pre-upgrade-check

Step 2: Rollback

When using a charm from charmhub:

juju refresh postgresql --revision=182

When deploying from a local charm file, one must have the previous revision charm file and run:

juju refresh postgresql --path=./postgresql_ubuntu-22.04-amd64.charm

Where postgresql_ubuntu-22.04-amd64.charm is the previous revision charm file.

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 revision.

Step 3: 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.


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