Perform a minor upgrade

Example: PostgreSQL 14.8 -> PostgreSQL 14.9
(including charm revision bump: e.g. Revision 193 -> Revision 196)

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

Key topics to take into consideration before upgrading.

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

Note

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

Important

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 the 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.

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

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.