[2.3+, UI] Changing a subnet's fabric/vlan doesn't automatically update the interface model

[Andres Rodriguez]

1. I had the following:

fabric-0.untagged - subnet1
fabric-1.untagged - <no subnet>

Rack controller interface:

ethX - fabric0 - untagged - subnet1

2. Then, I moved subnet1 (over the API) to fabric-1.untagged , which was successful.

3. I noticed that rack controller interface remainted as (1)

4. Restarted maas-rackd and interface now correctly shows:

ethX - fabric1 - untagged - subnet1

So that means MAAS is not automatically updating the interfaces when the network model changes.

[Mike Pontillo (mpontillo)]

We should further discuss how to properly handle this issue. In particular, if there are multiple subnets on a VLAN, and only one of them is moved, should we move *all* the subnets to the new VLAN? There might be a mix of multiple IPv4 and IPv6 subnets on the same VLAN. So we have to handle the following cases:

(1) The administrator just wants to move a single subnet to another VLAN.
(2) The administrator wants to move all subnets to another VLAN.

We could restrict the "change interfaces automatically" behavior so that it happens only if there is a single subnet on the VLAN.

Or we could not move interface VLANs automatically at all, like we do today, and just have the NetworksMonitoringService force-refresh to make sure rack controllers are at least up-to-date. Machines whose interfaces were automatically detected on a particular VLAN would need to be re-commissioning to update their information.

[Mike Pontillo (mpontillo)]

For now, I'll move forward assuming we're just going to force a refresh, to prevent users from having to restart the rack controller to re-detect the network after moving a subnet to another fabric/VLANs.