Report VM IP addresses to host agent

[jandubois]

Right now the only way to discover the IP address assigned to a vznat or vmnet interface is by running ip a inside the instance and parsing the output.

It would be nice if the guestagent would report this back to the hostagent, and limactl list could include this information.

[AkihiroSuda]

When the guestagent is not running (limactl create --plain), the IP field should be empty, or the hostagent should actively inspect the IP by running ssh INST ip a?

[jandubois]

Given that the host agent will still run the probe to verify that ssh is working, I guess we could also run the ip command.

I don't really like the idea of running non-probe scripts from the host agent, but on the other hand having the IP addresses for plain VMs could be very useful.

So I guess I'm voting for utility over purity.

[jandubois]

Off-topic, but maybe relevant for the implementation: Once we have a mechanism for the host agent to update the information provided by limactl list, we may want to include other information too. The obvious example would be the list of currently active port forwards.

So any mechanism to report the IP addresses from the agent should be flexible enough to include other info as well. I assume this will just be a JSON file in the instance directory that the host agent will update atomically whenever it has updated information. Then limactl list will know to ignore the file if the VM is not in Running state.

[afbjorklund]

I started on providing non-static information, in the status endpoint, but it was a while ago and didn't finish...

• Monitor guest activity using the agent #835