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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 same 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>

Note: All top-level runsc flags needed when calling run must be provided to restore.

How to use checkpoint/restore in Docker:

Run a container:

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

Checkpoint the container:

docker checkpoint create <container-name> <checkpoint-name>

Restore into the same container:

docker start --checkpoint <checkpoint-name> <container-name>

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. This is needed to support container migration.
  • 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.