While this is possible, it is not something we "support" upstream. We already have many combinations of OS distro and binary/source. I know that people have tried it in the past, and while it should mostly just work, occasionally it causes issues. A classic issue would be using an ansible fact about the host OS to infer something about the container. While we'll likely accept reasonable fixes for these issues upstream, mixing host and container OS may cause people to pay less attention to bugs raised.
Understood. If we run into issues, I'll report regardless of whether there is attention, just so someone knows what was tried, and what failed.
If you want to migrate from CentOS 7 to Debian, I would suggest keeping the host and container OS the same, by basing the kolla_base_distro variable on groups. Of course this will also be an untested configuration, and I suggest that you test it thoroughly, in particular things like migration between different versions of libvirt/qemu.
Ah, that's a good idea, setting kolla_base_distro in groups as opposed to globally. Thanks! If we can do that, then we'll definitely keep both host and container OS the same. We're testing in a VM environment first, so will try to identify problems before we have to do this on live systems. Thanks again for the quick responses as always Mark! Eric