Libvirt & Podman: follow up for Podman 4.0 and netavark

This is a follow up post to “Joining libvirt VMs and Podman container in a common network”. Therefore I won’t cover all the basics again and how to configure libvirt because nothing’s changed on that side.

Podman 4.0

Podman 4.0 comes with a completely new network stack replacing the previous CNI stack:

• Netavark
• Aardvark

There are great resources that explain the backgrounds of both tools and I don’t think I could describe it better than the folks implementing it :smile: so if you’re interested have a look at the aforementioned article or the release post.

Netavark and libvirt

After reading the announcement I was most curious if I would be able to configure an equivalent setup for Netavark like I described it with Podman 3.x and CNI.

Short answer: yes, it is possible! :tada:

“But how?!” do you ask? Well it’s pretty much equivalent to the previous solution: you need to create a new Podman network I once more named it ’libvirt’. To get an idea how the config should look like and where it should placed. I reused the CLI call from my previous article:

podman network create \
    --disable-dns \
    --internal \
    --gateway 10.10.2.37 \
    --ip-range 10.10.2.160/29 \
    --subnet 10.10.2.0/24 \
    libvirt

The configuration files are now obviously resided in /etc/containers/networks/ and my (already modified) libvirt.json now looks like so:

{
     "name": "libvirt",
     "id": "0489e6e643b97003c47b27a9ce0a6f6a8dce7d5f08329603e79a0ba48ad5285f",
     "driver": "bridge",
     "network_interface": "conbr0",
     "created": "2022-04-05T09:18:48.198960971+01:00",
     "subnets": [
          {
               "subnet": "10.10.1.0/24",
               "gateway": "10.10.1.42",
               "lease_range": {
                    "start_ip": "10.10.1.1",
                    "end_ip": "10.10.1.10"
               }
          }
     ],
     "ipv6_enabled": false,
     "internal": false,
     "dns_enabled": false,
     "ipam_options": {
          "driver": "host-local"
     }
}

Side note: I’m really happy they dropped the .conflist extension because this way most editors offer really helpful syntax highlighting in the first place!

Note that "internal": false is mandatory. Otherwise I wasn’t able to establish communication between VM and container. I also disabled the Aardvark DNS server and IPv6 support because I don’t need it and I also don’t expect much benefit of it due to the fact that it can’t be aware of the VMs present in the network same as dnsmasq won’t be able to resolve containers in the libvirt network.

Having this in place I was again able to reuse the CLI command from my previous article:

podman run \
    --rm \
    -d \
    --name nginx \
    --network libvirt \
    --ip 10.10.1.151 \
    docker.io/nginx:alpine

to create a Nginx container that can be reached from a VM.

Troubleshooting

Sometimes the communication between container and VM fails - don’t know if I restarted the libvirt network previously or somehow fucked up the container network configuration but a:

podman network reload <container ID/container name>

often resolved the problem.

Final thoughts

I haven’t used Netavark and Aardvark a lot, yet. But I already noticed a few really awesome things:

• the docker-compose support seems to be a lot better now because containers are actually able to talk to each other by service name, something I wasn’t able to configure properly in Podman 3.x - at least not rootless.
• with Netavark all the Podman configuration is now unified within /etc/containers or $HOME/.config/containers respectively
• the new configuration format is a little bit cleaner the the previous one due to the fact that Netavark does not support plugins and with a .json extension editors do help a lot more without requiring extra “configuration”