clh: Usage of REST APIs in Kata

[likebreath]

This issue tracks how the REST APIs provided by cloud-hypervisor is being used in Kata. We plan to integrate all REST APIs from CLH in Kata unless we don't find a valid use-case in the container land.

REST APIs being used

Action	Endpoint
Check for the REST API availability	/vmm.ping
Shut the VMM down	/vmm.shutdown
Create the VM	/vm.create
Boot the VM	/vm.boot
Dump the VM information	/vm.info
Add/remove CPUs to/from the VM	/vm.resize
Add VFIO PCI device to the VM	/vm.add-device
Add/remove memory from the VM	/vm.resize

REST APIs NOT being used

Action	Endpoint	Note
Delete the VM	/vm.delete	Probably would be nice to use as cleanup in driver
Shut the VM down	/vm.shutdown	Want it for force stop?
Reboot the VM	/vm.reboot	No use-case
Pause the VM	/vm.pause	Needed for VM templating #2557
Resume the VM	/vm.resume	Needed from VM templating #2557
Remove VFIO PCI device from the VM	/vm.remove-device	#2569
Add disk device to the VM	/vm.add-disk	Work-in-progress #2570
Add fs device to the VM	/vm.add-fs	All shared directories are mounted under the same path so only one fs dir is used in katal, not needed at the moment.
Add pmem device to the VM	/vm.add-pmem	Work-in-progress #2575
Add network device to the VM	/vm.add-net	May be needed for advanced CNI pluggins but not tests today to confirm, need to add test first and enable if needed.
Add vsock device to the VM	/vm.add-vsock	Kata works with vsock as could plug device, and we need this ready to allow the agent can connect so not a priority in kata.

[likebreath]

Please share if you have comments/advises/questions, epscially about REST APIs that are not being used.
/cc @jcvenegas @amshinde @sameo @sboeuf

[sboeuf]

@likebreath if there's no use case for some of the APIs, that's totally fine. Cloud-Hypervisor has a broader scope than just Kata, and Kata only uses the API that can fit in the container ecosystem.
Maybe pause/resume could have a use case, but I know that the container is already paused in the VM when that's needed.

[jcvenegas]

@likebreath @sboeuf probably we will want to use pause/resume for VM factory, this a use case were missing but not sure if is part of clh next items to add

[sboeuf]

@jcvenegas

but not sure if is part of clh next items to add

What do you mean? In terms of priority?
I'd say it's definitely not high priority (even from Kata's perspective), but it's ready from a CH perspective, so if this does not take too much effort to enable it for Kata, go for it :)

[amshinde]

@likebreath I think we do call the Remove method on vfio devices, so should make use of /vm.remove-device to implement that.

[likebreath]

@sboeuf @jcvenegas In the status update tomorrow, we can talk about whether the VM factory is something we want to include in the near future.
@amshinde Thanks for the comments on /vm.remove-device. I have put its status as To be added.

[likebreath]

Two more new APIs being added from CLH for the past month: /vm.add-fs and /vm.add-vsock.

As noted here, Kata prefers to start with minimum configurations and hot-plug devices on-the-fly as needed, Do we see potential benefits of hot-plugging vosck and/or virtio-fs devices?

/cc @jcvenegas