[devseed] Expand deployer exec homes command to optionally include EBS volumes for AWS clusters

[sgibson91]

We have a deployer exec homes command that creates a throwaway k8s pod with the home directories mounted from NFS with read-write access. As we migrate our AWS hubs to using in-cluster NFS backed by EBS volumes, we will also need to mount these data sources. Being able to do this will also assist with the migration process tracked in #4728 as we tried to mount the EFS instance to an EC2 instance but failed.

This issue tracks expansion of the deployer exec homes command to optionally include EBS volumes for AWS clusters.

Definition of Done

• deployer exec homes has an optional flag to also mount EBS volumes for AWS clusters
• when executed, the throwaway pod has access to both EFS and EBS file systems

[sunu]

@sgibson91 I've created a PR at #4803 to address this issue but it takes a slightly different approach.

I realized the jupyter-home-nfs NFS server pod and the throwaway pod could be running on different nodes. And we can't safely mount the EBS backed PVC created by jupyter-home-nfs to multiple nodes at once in read/write mode since EBS volumes don't support that.

Instead, I've added some optional arguments to the root_homes command so that we can mount an extra NFS backed volume to the throwaway pod. This should allow us to mount a volume backed by the existing EFS instance and another volume backed by the NFS server of jupyter-home-nfs to the same throwaway pod and migrate the data from one to the other.

Let me know if that sounds reasonable.

[sgibson91]

Yep, that sounds reasonable, thanks!