Checkpoint/Restore

gVisor has the ability to checkpoint a process, save its current state in a state file, and restore into a new container using the state file.

How to use checkpoint/restore

Checkpoint/restore functionality is currently available via raw runsc commands. To use the checkpoint command, first run a container.

runsc run <container id>

To checkpoint the container, the --image-path flag must be provided. This is the directory path within which the checkpoint state-file will be created. The file will be called checkpoint.img and necessary directories will be created if they do not yet exist.

Note: Two checkpoints cannot be saved to the save directory; every image-path provided must be unique.

runsc checkpoint --image-path=<path> <container id>

There is also an optional --leave-running flag that allows the container to continue to run after the checkpoint has been made. (By default, containers stop their processes after committing a checkpoint.)

Note: All top-level runsc flags needed when calling run must be provided to checkpoint if –leave-running is used.

Note: –leave-running functions by causing an immediate restore so the container, although will maintain its given container id, may have a different process id.

runsc checkpoint --image-path=<path> --leave-running <container id>

To restore, provide the image path to the checkpoint.img file created during the checkpoint. Because containers stop by default after checkpointing, restore needs to happen in a new container (restore is a command which parallels start).

runsc create <container id>

runsc restore --image-path=<path> <container id>

How to use checkpoint/restore in Docker:

Currently checkpoint/restore through runsc is not entirely compatible with Docker, although there has been progress made from both gVisor and Docker to enable compatibility. Here, we document the ideal workflow.

Run a container:

docker run [options] --runtime=runsc <image>`

Checkpoint a container:

docker checkpoint create <container> <checkpoint_name>`

Create a new container into which to restore:

docker create [options] --runtime=runsc <image>

Restore a container:

docker start --checkpoint --checkpoint-dir=<directory> <container>

Issues Preventing Compatibility with Docker

  • Moby #37360: Docker version 18.03.0-ce and earlier hangs when checkpointing and does not create the checkpoint. To successfully use this feature, install a custom version of docker-ce from the moby repository. This issue is caused by an improper implementation of the --leave-running flag. This issue is fixed in newer releases.
  • Docker does not support restoration into new containers: Docker currently expects the container which created the checkpoint to be the same container used to restore which is not possible in runsc. When Docker supports container migration and therefore restoration into new containers, this will be the flow.
  • Moby #37344: Docker does not currently support the --checkpoint-dir flag but this will be required when restoring from a checkpoint made in another container.