argo-workflows with urunc

[ciprian-barbu]

Hello,

Me and my team are trying to create workflows that run pods with a patched runtimeClassName, specifically urunc. This custom runtimeClass allows running unikernels as Kubernetes workloads, which means that instead of containers spawned from runc, there will be in fact qemu processes spawned by urunc.

The problem we are facing is better described in this issue on the urunc github:
nubificus/urunc#135

Briefly, our workflow is never ready, the Wait container does not detect that the Main container has finished. Because we use a different runtimeClass, not the default runc, we cannot run the argoexec binary inside our Main container, so urunc ignores the argoexec preamble.

We had some information exchanges with the urunc developers, but I think it is worth opening a discussion here.

To that end, I have a few questions:

1. What options do we have for overriding the runtimeClassName? So far we only had success with podSpecPatch, see this manifest
2. From our current understanding, argo waits for the Main container to finish, and it looks at a specific file. Are there better ways to do this check? Can't argo use Kubernetes APIs?
3. What does argoexec do that we are missing? Does it connect the dots with the Wait container by creating that file it needs?

I hope I didn't miss some important documentation, I'm fairly new with argo workflows.

Thanks and regards,
Ciprian