Note: All commands are written for juju >= v.3.0
If you are using an earlier version, check the Juju 3.0 Release Notes.
Perform a minor upgrade
Example: PostgreSQL 14.8 → PostgreSQL 14.9
(including charm revision bump: e.g. Revision 193 → Revision 196)
This guide is part of Charmed PostgreSQL Upgrades. Refer to this page for more information and an overview of the content.
Summary
- Pre-upgrade checks: Important information to consider before starting an upgrade.
- 1. Collect all necessary pre-upgrade information. It will be necessary for a rollback, if needed. Do not skip this step; better to be safe than sorry!
- 2. Prepare your Charmed PostgreSQL Juju application for the in-place upgrade. See the step details for all technical details executed by charm here.
- 3. Upgrade. Once started, all units in a cluster will be executed sequentially. The upgrade will be aborted (paused) if the unit upgrade has failed.
- 4. (Optional) Consider a rollback in case of disaster.
- Please inform us about your case scenario troubleshooting to trace the source of the issue and prevent it in the future.
- Post-upgrade check. Make sure all units are in the proper state and the cluster is healthy.
Pre-upgrade checks
Before performing a minor PostgreSQL upgrade, there are some important considerations to take into account:
- Concurrency with other operations during the upgrade
- Backing up your data
- Service disruption
Concurrency with other operations
We strongly recommend to NOT perform any other extraordinary operations on Charmed PostgreSQL cluster while upgrading.
Some examples are operations like (but not limited to) the following:
- Adding or removing units
- Creating or destroying new relations
- Changes in workload configuration
- Upgrading other connected/related/integrated applications simultaneously
Concurrency with other operations is not supported, and it can lead the cluster into inconsistent states.
Backups
Make sure to have a backup of your data when running any type of upgrade.
Guides on how to configure backups with S3-compatible storage can be found here.
Service disruption
It is recommended to deploy your application in conjunction with the Charmed PgBouncer operator.
This will ensure minimal service disruption, if any.
Step 1: Collect
This step is only valid when deploying from charmhub.
If a local charm is deployed (revision is small, e.g. 0-10), make sure the proper/current local revision of the .charm file is available BEFORE going further. You might need it for a rollback.
The first step is to record the revision of the running application as a safety measure for a rollback action. To accomplish this, run the juju status command and look for the deployed Charmed PostgreSQL revision in the command output, e.g.:
Model Controller Cloud/Region Version SLA Timestamp
welcome-lxd lxd localhost/localhost 3.1.6 unsupported 11:35:36+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 14.9 active 3 postgresql 14/candidate 330 no
Unit Workload Agent Machine Public address Ports Message
postgresql/3* active idle 3 10.3.217.74 5432/tcp
postgresql/4 active idle 4 10.3.217.95 5432/tcp
postgresql/5 active idle 5 10.3.217.108 5432/tcp
Machine State Address Inst id Base AZ Message
3 started 10.3.217.74 juju-d483b7-3 [email protected] Running
4 started 10.3.217.95 juju-d483b7-4 [email protected] Running
5 started 10.3.217.108 juju-d483b7-5 [email protected] Running
In this example, the current revision is 330. Store it safely to use in case of a rollback!
Step 2: Prepare
Before running the juju refresh command, it’s necessary to run the pre-upgrade-check action against the leader unit:
juju run postgresql/leader pre-upgrade-check
Make sure there are no errors in the result output.
This action will configure the charm to minimize the amount of primary switchover, among other preparations for a safe upgrade process. After successful execution, the charm is ready to be upgraded.
Step 3: Upgrade
Use the juju refresh command to trigger the charm upgrade process.
Example with channel selection:
juju refresh postgresql --channel 14/edge
Example with specific revision selection:
juju refresh postgresql --revision=342
Example with a local charm file:
juju refresh postgresql --path ./postgresql_ubuntu-22.04-amd64.charm
All units will be refreshed (i.e. receive new charm content), and the upgrade will execute one unit at a time.
Note: To reduce connection disruptions, the order in which the units are upgraded is based on roles:
First the replica units, then the sync-standby units, and lastly, the leader(or primary) unit.
juju status will look like similar to the output below:
Model Controller Cloud/Region Version SLA Timestamp
welcome-lxd lxd localhost/localhost 3.1.6 unsupported 11:36:18+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 14.9 active 3 postgresql 14/edge 331 no
Unit Workload Agent Machine Public address Ports Message
postgresql/3* waiting idle 3 10.3.217.74 5432/tcp other units upgrading first...
postgresql/4 waiting idle 4 10.3.217.95 5432/tcp other units upgrading first...
postgresql/5 waiting executing 5 10.3.217.108 5432/tcp waiting for database initialisation
Machine State Address Inst id Base AZ Message
3 started 10.3.217.74 juju-d483b7-3 [email protected] Running
4 started 10.3.217.95 juju-d483b7-4 [email protected] Running
5 started 10.3.217.108 juju-d483b7-5 [email protected] Running
After each unit completes the upgrade, the message will go blank, and a next unit will follow:
Model Controller Cloud/Region Version SLA Timestamp
welcome-lxd lxd localhost/localhost 3.1.6 unsupported 11:36:31+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 14.9 active 3 postgresql 14/edge 331 no
Unit Workload Agent Machine Public address Ports Message
postgresql/3* waiting idle 3 10.3.217.74 5432/tcp other units upgrading first...
postgresql/4 maintenance executing 4 10.3.217.95 5432/tcp refreshing the snap
postgresql/5 active idle 5 10.3.217.108 5432/tcp
Machine State Address Inst id Base AZ Message
3 started 10.3.217.74 juju-d483b7-3 [email protected] Running
4 started 10.3.217.95 juju-d483b7-4 [email protected] Running
5 started 10.3.217.108 juju-d483b7-5 [email protected] Running
Important Notes
Do NOT trigger rollback procedure during the running upgrade procedure.
It is expected to have some status changes during the process: waiting, maintenance, active.
Make sure upgrade has failed/stopped and cannot be fixed/continued before triggering rollback!
Please be patient during huge installations. Each unit should recover shortly after the upgrade, but time can vary depending on the amount of data written to the cluster while the unit was not part of it.
Incompatible charm revisions or dependencies will halt the process.
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 upgrade process will be halted and enter a failure state.
Step 4: Rollback (optional)
The step must be skipped if the upgrade went well!
Although 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.
Post-upgrade check
Future improvements are planned to check the state of a pod/cluster on a low level.
For now, use juju status to make sure the cluster state is OK.