If anybody is searching for how to perform a graceful switchover of you Live Master Postgresql to your secondary here’s how to do it:
Ensure the command is run against the Leader unit. From the juju status output the unit with the * is the leader:
root@maas-01:~# juju status
Model Controller Cloud/Region Version SLA Timestamp
postgresql-home lab.devzero.home-default lab.devzero.home/default 2.8.1 unsupported 22:34:55Z
App Version Status Scale Charm Store Rev OS Notes
postgresql 12.5 active 2 postgresql jujucharms 208 ubuntu
Unit Workload Agent Machine Public address Ports Message
postgresql/0 active idle 0 192.168.51.30 5432/tcp Live master (12.5)
postgresql/1* active idle 1 192.168.51.3 5432/tcp Live secondary (12.5)
Machine State DNS Inst id Series AZ Message
0 started 192.168.51.30 postgresql-0 focal AZ-1 Deployed
1 started 192.168.51.3 postgresql-1 focal AZ-2 Deployed
The exact context to turn postgresql/1 to the master
The reason for this post is the required switchover arguments aren’t clear from the juju actions output on the cli or on Charms homepage / documentation in the store.
I was lucky enough to stumble upon the required arguments on this unrelated post in discourse.
For a new Juju user this type of thing will be infuriating and probably be the reason they abandon using Juju.
That would be my expectation. If the Charm supports actions there should be a section on the Charms homepage covering what the actions do with a couple of examples.
I’m really thinking that the charmstore should present the actions.yaml schema data in a useful way in the same manner it does config.yaml.
The schema of actions.yaml is quite clear as to what the action does and the required parameter, but the auto-documentation of charmstore doesn’t really spell this out.
I would agree, temporarily, it may be helpful to put this change into the README for the charm, but I think it’d benefit all charms to have action schema documentation be made readable as documentation on charmstore.
While it’s not a user-friendly interface to this kind of documentation, adding --schema to juju actions command can help you determine the required and available params of a charm’s actions.
juju actions --schema postgresql
*snip*
switchover:
description: |
Promote a specific unit to master. Must be run on the leader unit.
properties:
master:
description: Unit to promote to master (eg. postgresql/3).
type: string
required:
- master
title: switchover
type: object
*snip*
@afreiberger we are actually currently migrating charms to the new charmhub.io . If a charm has a actions.yaml it should appear in the details page of the charm, see the action tab.
Currently not all charms are imported and may not have their actions.yaml imported too, but we are on it
A cosmetic note for actions in charmhub.io is that parameters that are required could just be marked as such rather than repeated in a section below. It’s more clean and less scrolling etc.
The new charmhub mechanism for docs managed as discourse topics is really nice. We are polishing up the navigation / index format at the moment but I really like how it has come together.
In addition to the improvements already mentioned; the Juju Dashboard will be gaining the ability to list, initiate, and monitor actions in the new year. We will be sure to post here once that’s available.
