DockerCLI/experimental/checkpoint-restore.md

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# Docker Checkpoint & Restore
Checkpoint & Restore is a new feature that allows you to freeze a running
container by checkpointing it, which turns its state into a collection of files
on disk. Later, the container can be restored from the point it was frozen.
This is accomplished using a tool called [CRIU](http://criu.org), which is an
external dependency of this feature. A good overview of the history of
checkpoint and restore in Docker is available in this
[Kubernetes blog post](http://blog.kubernetes.io/2015/07/how-did-quake-demo-from-dockercon-work.html).
## Installing CRIU
If you use a Debian system, you can add the CRIU PPA and install with apt-get
[from the criu launchpad](https://launchpad.net/~criu/+archive/ubuntu/ppa).
Alternatively, you can [build CRIU from source](http://criu.org/Installation).
You need at least version 2.0 of CRIU to run checkpoint/restore in Docker.
## Use cases for checkpoint & restore
This feature is currently focused on single-host use cases for checkpoint and
restore. Here are a few:
- Restarting the host machine without stopping/starting containers
- Speeding up the start time of slow start applications
- "Rewinding" processes to an earlier point in time
- "Forensic debugging" of running processes
Another primary use case of checkpoint & restore outside of Docker is the live
migration of a server from one machine to another. This is possible with the
current implementation, but not currently a priority (and so the workflow is
not optimized for the task).
## Using checkpoint & restore
A new top level command `docker checkpoint` is introduced, with three subcommands:
- `create` (creates a new checkpoint)
- `ls` (lists existing checkpoints)
- `rm` (deletes an existing checkpoint)
Additionally, a `--checkpoint` flag is added to the container start command.
The options for checkpoint create:
Usage: docker checkpoint create [OPTIONS] CONTAINER CHECKPOINT
Create a checkpoint from a running container
--leave-running=false Leave the container running after checkpoint
--checkpoint-dir Use a custom checkpoint storage directory
And to restore a container:
Usage: docker start --checkpoint CHECKPOINT_ID [OTHER OPTIONS] CONTAINER
A simple example of using checkpoint & restore on a container:
$ docker run --security-opt=seccomp:unconfined --name cr -d busybox /bin/sh -c 'i=0; while true; do echo $i; i=$(expr $i + 1); sleep 1; done'
> abc0123
$ docker checkpoint create cr checkpoint1
# <later>
$ docker start --checkpoint checkpoint1 cr
> abc0123
This process just logs an incrementing counter to stdout. If you `docker logs`
in between running/checkpoint/restoring you should see that the counter
increases while the process is running, stops while it's checkpointed, and
resumes from the point it left off once you restore.
## Current limitation
seccomp is only supported by CRIU in very up to date kernels.
External terminal (i.e. `docker run -t ..`) is not supported at the moment.
If you try to create a checkpoint for a container with an external terminal,
it would fail:
$ docker checkpoint create cr checkpoint1
Error response from daemon: Cannot checkpoint container c1: rpc error: code = 2 desc = exit status 1: "criu failed: type NOTIFY errno 0\nlog file: /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log\n"
$ cat /var/lib/docker/containers/eb62ebdbf237ce1a8736d2ae3c7d88601fc0a50235b0ba767b559a1f3c5a600b/checkpoints/checkpoint1/criu.work/dump.log
Error (mount.c:740): mnt: 126:./dev/console doesn't have a proper root mount