Add support for container restore from a checkpoint in Kubernetes

[rst0git]

containerd provides native support for checkpoint/restore using checkpoint images. The more recently introduced functionality that connects the existing checkpoint functions to the CRI ContainerCheckpoint RPC allows to export the 1) CRIU data, 2) rootfs diff, and 3) spec from the checkpoint image into a tar archive. This tar archive has format similar to the one used by CRI-O. However, since containerd has native support for checkpoint images and CRI-O does not, it is unclear how to enable the restore functionality.

There are two approaches that we could use to enable container restore with containerd in Kubernetes:

1. We can use a tool such as checkpointctl to create a checkpoint image in the format currently used by containerd, or
2. Modify containerd to support restore with the checkpoint image format used by CRI-O.

@adrianreber @estesp Do you have any advice or recommendations on which approach might be more suitable?

cc: @liunan-ms @viktoriaas