network interruption when there is no change on the netplan config

[Hua Zhang]

Network interruption may occur even when there is no change on the netplan config. eg: when running 'juju config ovn-chassis sriov-numvfs=enp94s0f1:16' to change VF number, it will generate a netplan config file /etc/netplan/150-charm-ovn.yaml . Even if the netplan configs remains unchanged afterwards, running 'netplan apply' can still cause network interruption.

I checked the code [1], it has the following code comment:

        # Re-start service when
        # 1. We have configuration files for it
        # 2. Previously we had config files for it but not anymore
        # Ideally we should compare the content of the *netplan-* files before and
        # after generation to minimize the number of re-starts, but the conditions
        # above works too.

So running 'netplan apply' will cause a networkd restart if there are existing *netplan-* files present. I think we had better compare the content of the *netplan-* files before and after generation to minimize the number of re-starts.

[What is known and has been done so far?]
A snippet from the syslog
https://paste.ubuntu.com/p/4Y49tRxf95/

[Distribution/Release, Package versions, Platform]
Jammy/Yoga

[Steps to Reproduce]
'netplan apply'

[1] https://github.com/canonical/netplan/blob/main/netplan_cli/cli/commands/apply.py#L137

[Lukas Märdian (slyon)]

Yes, Netplan should implement improved/seamless "netplan apply" and only re-configure interfaces that actually changes, instead of re-configuring all interfaces or re-starting the full networking daemon.

(See FR-3700)