KVM Hosts Deleted off filesystem when VM host/rack connects to a different MAAS

[Lee Trager]

A MAAS user deployed an 18.04 libvirt KVM host with MAAS 2.6.2. They then installed a MAAS 2.6.2 rack controller on the KVM host they just deployed. They setup a parallel MAAS 2.9.2 environment by cloning the database the MAAS 2.6.2 used. They turned off DHCP on one VLAN in the MAAS 2.6.2 environment so they could enable it in the MAAS 2.9.2 environment. They then connected the rack controller, running MAAS 2.6.2 to the MAAS 2.9.2 environment. This resulted in both VMs on the libvirt KVM host being deleted. The VMs remained modeled in both MAASes.

Attempting to connect one rack controller to two different MASSs is not possible. Connecting a MAAS 2.6.2 rack to a MAAS 2.9.2 region is incorrect and should be prevented(LP:1916089). MAAS should never delete a VM unless explicitly told to by the user.

[Lee Trager (ltrager)]

I'm unable to reproduce this. I've tried various methods.

[Alberto Donato (ack)]

In the upcoming 3.0 release, MAAS doesn't delete VMs when the KVM host is removed unless decompose=True is passed

[Alberto Donato (ack)]

But I wonder what's happened here exactly, removing VMs when registering a host was never MAAS' behavior.
Up until 2.9, VMs are decomposed when the host is removed if they were composed by MAAS.

[Björn Tillenius (bjornt)]

We need to know how the kvm pod was registered. If it was registered pointing to 'localhost', it makes sense. And we shouldn't allow localhost to be used when registering a kvm pod.