Comment 3 for bug 1964644

As discussed on the channel today, I deployed a brand new machine with MAAS 3.1 Snap (3.1.0-10901-g.f1f8f1505), PostgreSQL 12 outside of snap and initialized it as region+rack controller. The configured subnet was 10.1.10.0/24 (IP: 10.1.10.254/24).

The test involved two scenarios:

Scenario 1)

- Used a blank installed 20.04 LTS + PostgreSQL 12 + MAAS 3.1 Snap (3.1.0-10901-g.f1f8f1505)
- Went through MAAS initial setup screen.
- Changed network discovery interval to 10 minutes.
- Edited machines' netplan configuration, switching subnet from /24 to /22
- Rebooted the machine, a new 10.1.8.0/22 subnet was added under subnets/fabric-0 next to the existing 10.1.10.0/24 (See logs package for screenshots)

Scenario 2)

- Used a blank installed 20.04 LTS + PostgreSQL 12 + MAAS 3.1 Snap (3.1.0-10901-g.f1f8f1505)
- Went through MAAS initial setup screen.
- Changed network discovery interval to 10 minutes.
- From MAAS WebUI, Subnets tab, Changed 10.1.10.0/24 subnet to 10.1.8.0/22
- No new subnets were added besides 10.1.8.0/22

The logs package includes:

- Logs for scenario 1 and 2 captured from /var/snap/maas/common/log/
- Screenshots from scenario 1

This process was repeated twice with the exact same results.

Hope this helps to shed a bit of light on the issue.