bug: maas_url is not updated when pointing to an offline region controller

[skatsaounis]

Steps to reproduce

1. Install maas-region+maas-agent+haproxy+keepalived for haproxy VIP on three machines
2. Poweroff the machine with the haproxy unit whose public address is picked up to form maas_url
3. Try to commission a machine with MAAS, or deploy or download an image

Expected behavior

Everything works fine.

Actual behavior

MAAS on two active machines continue to use the offline node's ip inside their maas_url. As such, MAAS agents which are part of rack controllers from 3.5 are not able to communicate with the online region controllers. MAAS is not operational.

Versions

Operating system: Ubuntu 22.04

Juju CLI: 3.4.5

Juju agent: 3.4.5

Charm revisions:

maas-region: 16 (3.5/edge)
maas-region: 12 (3.5/edge)

Log output

Juju debug log: N/A

Additional context