26. Check in_progress

Operations to run while in progress

While a refresh is in progress, the application is in a vulnerable state and (while units restart) performance may be degraded. Also, it is important that the user is able to quickly rollback at any time while a refresh is in progress.

With this in mind, some operations should be forbidden while a refresh is in progress—​because they could be dangerous, because they are non-essential, or because they could slow down a rollback.

Examples of operations that might be forbidden (depends on the workload; these examples might be incorrect for some workloads):

  • Creating a backup

  • Restoring a backup

  • Rotating passwords/certificates

  • Changing config options

At the same time, the application must:

Maintain high availability while refresh is in progress (for up to multiple weeks)

4. Product requirements

Therefore, the charm code must handle critical operations while a refresh is in progress. For example:

  • IP address changes

  • Scaling the application up or down

Check if a refresh is in progress

Example
class PostgreSQLCharm(ops.CharmBase):
    refresh: charm_refresh.Common

    def _restore_backup(self, event: ops.ActionEvent):
        if self.refresh.in_progress:
            event.fail("Refresh in progress")
            return