Unsafe network parent in use check

[edlerd]

Required information

• Distribution: snap
• Distribution version: lxd git-4010d6d 32032 latest/edge

Issue description

On cluster networking: I can sometimes use the same physical interface from a cluster member for two physical managed networks. In other times I get an error: Parent interface in use by another network. I think the error should always be displayed.

Suspecting the parent in use function to be insufficient in the cluster case. It should likely be loading the network configuration for each cluster member and ensure no parent interface collisions per member.

Steps to reproduce

1. LXD Cluster of 3 members: m1, m2 and m3. m1 and m2 have two interfaces i1 and i2, m3 has one interface (m3 having only one interface might not be relevant)
2. Create a physical network n1 using interface i1 on all members
3. Create another physical network n2 using interface i2 on member m1, and interface i1 on m2 and m3. Issue this command against m1.
4. No error is displayed, even though we are already using i1 on n1 for the members m2 and m3.

[edlerd]

An open, related question is: Is there a situation, where the same physical non-managed interface is used as a parent for more than one physical managed network? Or should the interfaces be used for a maximum of one time?

Motivation for the question is that in the LXD-UI. We could disable any already used interface in the parent selector if an interface may be used only once as a parent.

[tomponline]

Is there a situation, where the same physical non-managed interface is used as a parent for more than one physical managed network? Or should the interfaces be used for a maximum of one time?

I think:

the interfaces be used for a maximum of one time