Failing to initialize maas-region on machines that maas-agent pre-exists or is initialized faster

[skatsaounis]

Steps to reproduce

juju deploy postgresql --channel 14/candidate --revision 553 --to 7 --config experimental_max_connections=250 --config plugin_audit_enable=false
juju deploy maas-region --channel 3.5/edge --to 8
juju integrate postgresql maas-region
juju add-unit maas-region -n 2 --to 9,10
juju deploy maas-agent --channel 3.5/edge -n 3 --to 8,9,10
juju integrate maas-agent maas-region

Expected behavior

Splitting the installation of maas-region to two phases to overcome #315 , I would expect that a 3 node MAAS region+rack cluster is initialized successfully.

Actual behavior

It seems that if maas-agent is installed first, it binds the ports before maas-region. As a result, the initialization of the MAAS cluster is incomplete.

Versions

Operating system: Jammy 22.04

Juju CLI: 3.6.2-genericlinux-amd64

Juju agent: 3.6.2

Charm revision:
maas-region: 74
maas-agent: 12

Log output

2025-01-29 14:44:36 ERROR unit.maas-region/4.juju-log server.go:326 failed to open service ports
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-maas-region-4/charm/venv/ops/model.py", line 3319, in _run
    result = subprocess.run(args, **kwargs)  # type: ignore
  File "/usr/lib/python3.10/subprocess.py", line 526, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '('/var/lib/juju/tools/unit-maas-region-4/open-port', '53/udp')' returned non-zero exit status 1.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-maas-region-4/charm/./src/charm.py", line 227, in _setup_network
    self.unit.set_ports(*MAAS_REGION_PORTS)
  File "/var/lib/juju/agents/unit-maas-region-4/charm/venv/ops/model.py", line 803, in set_ports
    self._backend.open_port(protocol, port)
  File "/var/lib/juju/agents/unit-maas-region-4/charm/venv/ops/model.py", line 3802, in open_port
    self._run('open-port', arg)
  File "/var/lib/juju/agents/unit-maas-region-4/charm/venv/ops/model.py", line 3321, in _run
    raise ModelError(e.stderr) from e
ops.model.ModelError: ERROR cannot open 53/udp (unit "maas-region/4"): port range conflicts with 53/udp (unit "maas-agent/4")

2025-01-29 14:44:37 INFO juju.worker.uniter.operation runhook.go:186 ran "start" hook (via hook dispatching script: dispatch)

Additional context