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Line 1: − == Introduction ==+ + + + + + − + − Docker 1.5 [https://github.com/SaiedKazemi/docker/wiki]+ − Docker 1.7 [https://github.com/boucher/docker/tree/cr-combined] − }} − + − + − + Line 21:
Line 24: − {{Note| External C/R was done as proof-of-concept. Its use is discouraged and the helper script mentioned below will be deprecated in the near future.}}+ − − − Because the Docker daemon is involved in both checkpoint and restore,+ − + − + − + − + − + + + + − Work in underway to integrate C/R into the new <code>libcontainer</code>. − For native C/R support, additional functionality was added to CRIU.+ − The most notable addition is the <code>--inherit-fd</code> command line option.+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Line 104:
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Line 326: − − == OverlayFS == − − The OverlayFS filesystem was merged into the upstream Linux kernel 3.18 and is now Docker's preferred filesystem (instead of AUFS). For successful C/R, however, you need to apply the following kernel patch: − − OverlayFS patch [https://lkml.org/lkml/2015/3/20/372] − − == Async IO (AIO) == − − If you are using a kernel older than 3.19 and your container uses AIO, you need the following AIO kernel patches from 3.19: − − * {{torvalds.git|bd9b51e7}} by Al Viro − * {{torvalds.git|e4a0d3e72}} by Pavel Emelyanov −
no edit summary
This HOWTO page describes how to checkpoint and restore a Docker container.
This HOWTO page describes how to checkpoint and restore a Docker container.
{{Note| This page was originally written a few months ago. Since then, interfacing with CRIU has been added to Docker's native exec driver (libcontainer) and pull requests to add checkpoint/restore functionality to Docker have been submitted. If you just want to experiment with C/R, you can use one of the following Docker versions for your C/R experiments:
Docker 1.5 [https://github.com/SaiedKazemi/docker/wiki]
Docker 1.7 [https://github.com/boucher/docker/tree/cr-combined]}}
{{OverlayFS| The OverlayFS filesystem was merged into the upstream Linux kernel 3.18 and is now Docker's preferred filesystem (instead of AUFS). However, there is a bug in OverlayFS that reports the wrong mnt_id in /proc/<pid>/fdinfo/<fd> and the wrong symlink target path for /proc/<pid>/<fd>. Fortunately, these bugs have been fixed in the kernel v4.2-rc2. See below for instructions on how to apply the relevant patches.}}
{{Note| This page was originally written a few months ago. Since then, interfacing with CRIU has been added to Docker's native exec driver (libcontainer) and pull requests to add checkpoint/restore functionality to Docker have been submitted. You can use one of the following Docker versions for your C/R experiments:
{{Async IO| If your process uses async IO and your kernel is older than 3.19, you need to apply two patches. See below for instructions.}}
== Introduction ==
There are two ways to checkpoint and restore a Docker container:
There are two ways to checkpoint and restore a Docker container:
'''External C/R''' using CRIU directly on the command line as it's typically
'''1. External C/R''' using CRIU directly on the command line as it's typically
done.
done for any process tree.
This is called external because it's happening external to the
This approach is called external because it's happening external to the
Docker daemon. After checkpoint, the Docker daemon thinks that the
Docker daemon. After checkpoint, the Docker daemon thinks that the
container has exited. After restore, the Docker daemon doesn't know that
container has exited. After restore, the Docker daemon doesn't know that
will not work correctly.
will not work correctly.
'''2. Native C/R''' using new <code>docker checkpoint</code> and
'''Native C/R''' using the newly added <code>docker checkpoint</code> and
<code>docker restore</code> commands.
<code>docker restore</code> commands.
This approach is called native because the Docker daemon is involved in both checkpoint and restore.
its notion of the container state will be consistent and all commands such as
Therefore, its notion of the container state will be corrent. All commands such as
<code>docker ps, stop, kill </code> and <code>logs</code> will work.
<code>docker ps, stop, kill </code> and <code>logs</code> will work.
This is obviously the preferred method of checkpointing and restoring Docker containers.
This is obviously the preferred method of checkpointing and restoring Docker containers.
Native C/R is work in progress, say pre-alpha quality. You can
Native C/R is work in progress, say pre-alpha quality.
watch this short demo
You can watch this short demo
'''[https://www.youtube.com/watch?v=HFt9v6yqsXo video]'''
'''[https://www.youtube.com/watch?v=HFt9v6yqsXo video]'''
to see how it works. Source files for Docker 1.5 C/R are at this
to see how it works.
'''[https://github.com/SaiedKazemi/docker/tree/cr repo]'''.
Source files for Docker 1.5 C/R are
'''[https://github.com/SaiedKazemi/docker/tree/cr here]'''
and for Docker 1.7 C/R are
'''https://github.com/boucher/docker/tree/cr-combined here]'''.
The '''[https://github.com/SaiedKazemi/docker/wiki wiki]'''
The '''[https://github.com/SaiedKazemi/docker/wiki wiki]'''
page provides an overview of the project history.
page provides an overview of the project history.
== OverlayFS ==
The following small kernel patches fix the mount id and symlink target path issues noted above:
* {{torvalds.git|155e35d4da}} by David Howells
* {{torvalds.git|df1a085af1}} by David Howells
* {{torvalds.git|f25801ee46}} by David Howells
* {{torvalds.git|4bacc9c923}} by David Howells
* {{torvalds.git|9391dd00d1}} by Al Viro
Assuming that you are running Ubuntu Vivid (Linux kernel 3.19), here is how you can patch your kernel:
<pre>
git clone git://kernel.ubuntu.com/ubuntu/ubuntu-vivid.git
cd ubuntu-vivid
git remote add torvalds git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git remote update
git cherry-pick 155e35d4da
git cherry-pick df1a085af1
git cherry-pick f25801ee46
git cherry-pick 4bacc9c923
git cherry-pick 9391dd00d1
cp /boot/config-$(uname -r) .config
make olddefconfig
make -j 8 bzImage modules
sudo make install modules_install
sudo reboot
</pre>
== Async IO (AIO) ==
If you are using a kernel older than 3.19 and your container uses AIO, you need the following AIO kernel patches from 3.19:
* {{torvalds.git|bd9b51e79c}} by Al Viro
* {{torvalds.git|e4a0d3e720}} by Pavel Emelyanov
== External C/R ==
== External C/R ==
{{Note| External C/R was done as proof-of-concept. Its use is discouraged and the helper script mentioned below will be deprecated in the near future.}}
Starting with CRIU 1.3, it is possible to checkpoint and restore a
Starting with CRIU 1.3, it is possible to checkpoint and restore a
the global <code>/dev/null</code> and the container <code>/dev/null</code> as the same device.
the global <code>/dev/null</code> and the container <code>/dev/null</code> as the same device.
== Restore Prework ==
=== <code>--inherit-fd</code> ===
For native C/R support, this option tells CRIU to let the restored process "inherit"
its specified file descriptor (instead of restoring from checkpoint).
== Restore Prework for External C/R ==
As mentioned earlier, by default Docker uses AUFS to set up the
As mentioned earlier, by default Docker uses AUFS to set up the
to set up the filesystem again before attempting to restore.
to set up the filesystem again before attempting to restore.
== An Example ==
== An External C/R Example ==
Below is an example to show C/R operations for a shell script that
Below is an example to show C/R operations for a shell script that
</pre>
</pre>
== Helper Script ==
== External C/R Helper Script ==
As seen in the above examples, the CRIU command line for checkpointing and
As seen in the above examples, the CRIU command line for checkpointing and
root 6206 1 1 10:49 ? 00:00:00 /bin/sh -c i=0; while true; do echo $i >> /foo; i=$(expr $i + 1); sleep 3; done
root 6206 1 1 10:49 ? 00:00:00 /bin/sh -c i=0; while true; do echo $i >> /foo; i=$(expr $i + 1); sleep 3; done
</pre>
</pre>
[[Category:HOWTO]]
[[Category:HOWTO]]