Instruct NetPlan to use systemd-networkd

[hanwen-cluster]

Description of changes

systemd-networkd is used by default with Ubuntu Server. Installing ubuntu-desktop (as part of DCV installation) installs NetworkManager. NetworkManager is more complex (with WiFi capabilities) and causes confusion to systemd-networkd. When systemd-networkd is confused, it delays system boot by 2 minutes.

This commit instructs NetPlan to use systemd-networkd to manage network interfaces. The code is added at the end of DCV installation because the mitigation is strictly related to the installation of ubuntu-desktop. Always using systemd-networkd also improves consistency between how ParallelCluster handles single-nic instances vs multi-nic instances. With multi-nic instances ParallelCluster has been instructing netplan to use systemd-networkd (code)

Technical details:

Output of networkctl list

Prior to this commit

Base Ubuntu:

IDX LINK TYPE     OPERATIONAL SETUP
  1 lo   loopback carrier     unmanaged
  2 ens5 ether    routable    configured

2 links listed.

Ubuntu with ubuntu-desktop

IDX LINK TYPE     OPERATIONAL SETUP
  1 lo   loopback carrier     unmanaged
  2 ens5 ether    routable    unmanaged

2 links listed.

systemd-networkd got confused because it saw no network interface was setup (because NetworkManager took over control of all network interfaces) and waited until 2 minutes timeout at the beginning of system boot:

$ journalctl -b | grep -i "ipv6\|timeout\|waiting"
...
Sep 18 14:51:23 systemd-networkd-wait-online[1602]: Timeout occurred while waiting for network connectivity.
...
Sep 18 14:53:31 systemd-networkd-wait-online[1891]: Timeout occurred while waiting for network connectivity.
...

After this commit

Ubuntu with ubuntu-desktop has the same output as Base Ubuntu and the delay is gone

Tests

• Test with DCV has passed on both Ubuntu 22 and 24
• Test with multiple-NICs instances has passed on both Ubuntu 22 and 24

References

• Link to impacted open issues.
• Link to related PRs in other packages (i.e. cookbook, node).
• Link to documentation useful to understand the changes.

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

Please review the guidelines for contributing and Pull Request Instructions.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[hgreebe]

Is there any other side effect to having it use systemd-networkd instead of Network Manager or is it that Network Manager should have never been used for this purpose?

[hanwen-cluster]

Network Manager should have never been used for cloud instances. Mainly because cloud instances don't have WiFi.

I don't think we should be concerned about any side-effect, because we already configure multi-nics instances with systemd-networkd