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

[songponssw]

I'd like to volunteer for this task, if that's okay.

[jandubois]

I'd like to volunteer for this task, if that's okay.

Thank you for volunteering! I would suggest to write up your plan first and discuss it here in the issue before starting on the implementation.

[songponssw]

Goal

• Report the IP address from the guest back to the host agent.
• Implement a generic format and reporting mechanism between the guestagent and hostagent.

Design

• Add a subcommand on guestagent to collect instance information and metrics, and output it.
• Use limactl shell to execute this command from the host and capture the result.

Implementation Details

1. limaguestagent subcommand

• This command collects information and metrics from inside the instance.
• The output will be printed to the console.
• Metrics to include:
  • In this PR: IP address and currently listening ports.

2. Passing output to the host

• Use limactl shell to run the report command from the host.
• The output can be exported as JSON and saved into instance dir.

3. Add IP address to limactl ls

[AkihiroSuda]

Shell doesn't need to be used when the guestagent events are available

lima/pkg/guestagent/api/guestservice.proto

Line 19 in 7196333

message Event {

[AkihiroSuda]

And in the plain mode the guestagent binary is missing, so you'll have to run a plain shell script

[jandubois]

My suggestion would be to run ip -j a and ip -j r inside the guest and send the raw output to the host agent, which can then figure out how to process/report it. That way we don't need to parse stuff using shell inside the guest.

You do it over ssh in plain mode; otherwise the guestagent runs it and reports back over the direct connection.

I'm not sure if we need a mechanism to re-run the commands to update the information? E.g. I don't know if the IP address of a bridged socket_vmnet interface will change when the host (laptop) moves to a different network and gets new DHCP leases.

Using ip -j requires ip from iproute2. We would need to add it to our alpine-iso image, but I've verified that it is present in the regular Alpine cloud image, and I think it will be in all other modern Linux releases as well.

[AkihiroSuda]

Why not just use https://pkg.go.dev/net#Interfaces

[jandubois]

Why not just use https://pkg.go.dev/net#Interfaces

How do you do this from bash (when you don't have a guest agent)?

I thought it makes sense to use the same guest code, regardless on how the information is transported back to the host agent.