[CentOS-virt] OS-level virtualization using LXC and systemd-nspawn containers

Tue Jan 26 16:41:42 UTC 2021
Scott Dowdle <dowdle at montanalinux.org>


----- Original Message -----
> > LXD is a management layer on top of it which provides for easy
> > clustering and even managing VMs.  I think it is the closest thing
> > to vzctl/prlctl from OpenVZ.
> "Yes, you could use LXC without LXD. But you probably would not want to.
> On its own, LXC will give you only a basic subset of features.
> For a production environment, you’ll want to use LXD".

Have you tried LXD?  Again, I'd only recommend it on Ubuntu LTS and I believe your target is CentOS so that is probably why you are excluding it, eh?

> podman is replacement for Docker,
> it is not replacement for OpenVZ 6 containers.

Docker definitely targets "Application Containers"... with one service per container.  podman says they can also do "System Containers" by running systemd as the entry point.  Of course the vast majority of pre-made container images you'll find in container image repositories aren't built for that, but you can use distro provided images and build a system container image out of them.  I have a simple recipe for Fedora, CentOS, and Ubuntu.  I don't know how many people are using podman in this capacity yet, and I don't know if it is mature or not for production... but the limited testing I've done with it, has worked out fairly well... using Fedora or CentOS Stream 8 as the host OS... and yes, even running the container as a regular user after doing:

setsebool -P container_manage_cgroup on

Yes, podman does still use it's own private network addressing, but I guess that can be overcome by telling it to use the host network.  I haven't tried that.  Not exactly like OpenVZ's container networking for sure.

> I have containers with 1.6 TiB of valuable data - podman
> not designed to work in this mode and in such conditions.

Persistent data really isn't an issue.  You just have to understand how it works.  Plenty of people run long-term / persistent-data Docker and podman containers... although granted, most folks say if you are using persistent data containers, you are doing it wrong.  I guess I prefer to do it wrong. :)

> So I have only two alternatives for OS-level virtualization:
> LXC or systemd-nspawn.

If CentOS is your target host, I'd guess that neither of those really are a good solutions... simply because they aren't supported and upstream doesn't care about anything other than podman for containers.

LXC varies from one distro to the next... with different kernels, and different versions of libraries and management scripts.  Again, LXD on an Ubuntu LTS host is probably the most stable... with Proxmox VE as a close second.  Both of those upstreams care about system containers and put in a lot of effort to make it work.

Good luck.

Scott Dowdle
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Belgrade, MT 59714
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