mirror of
https://github.com/moby/moby.git
synced 2022-11-09 12:21:53 -05:00
87 lines
3.5 KiB
Markdown
87 lines
3.5 KiB
Markdown
# 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 commands `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 [OPTIONS] CONTAINER CHECKPOINT_ID
|
|
|
|
Checkpoint the specified container
|
|
|
|
--leave-running=false leave the container running after checkpoint
|
|
|
|
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
|
|
|