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Line 1: − This article describes how to perform checkpoint-restore for an LXC container.+ − == Preparing a Linux Container ==+ − + − * A console should be disabled (<code>lxc.console = none</code>)+ − * udev should not run inside containers (<code>mv /sbin/udevd{,.bcp}</code>)+ + + + + − === Preparing a host environment ===+ − * Mount cgroupfs+ − $ mount -t cgroup c /cgroup + + − * Create a network bridge+ − # cat /etc/sysconfig/network-scripts/ifcfg-br0 − DEVICE=br0 − TYPE=Bridge − BOOTPROTO=dhcp − ONBOOT=yes − DELAY=5 − NM_CONTROLLED=n − $ cat /etc/sysconfig/network-scripts/ifcfg-eth0 − DEVICE="eth0" − NM_CONTROLLED="no" − ONBOOT="yes" − BRIDGE=br0 − + − * Download an OpenVZ template and extract it.+ − <pre><nowiki>curl http://download.openvz.org/template/precreated/centos-6-x86_64.tar.gz | tar -xz -C test-lxc+ − </nowiki></pre>+ − * Create config files+ − $ cat ~/test-lxc.conf + − lxc.console=none+ − lxc.utsname = test-lxc+ − lxc.network.type = veth − lxc.network.flags = up − lxc.network.link = br0 − lxc.network.name = eth0 − lxc.mount = /root/test-lxc/etc/fstab − lxc.rootfs = /root/test-lxc-root/ − $ cat /root/test-lxc/etc/fstab+ − none /root/test-lxc-root/dev/pts devpts defaults 0 0 − none /root/test-lxc-root/proc proc defaults 0 0 − none /root/test-lxc-root/sys sysfs defaults 0 0 − none /root/test-lxc-root/dev/shm tmpfs defaults 0 0 − * Register the container+ − $ lxc-create -n test-lxc -f test-lxc.conf+ + + + − * Start the container+ − $ mount --bind test-lxc test-lxc-root/ − $ lxc-start -n test-lxc − + + + − === Preparations ===+ − You not only need to [[Installation | install]] the crtools, but also check that the iproute2 utility (<code>ip</code>) is v3.6.0 or higher.+ + + − You can clone the [http://git.kernel.org/?p=linux/kernel/git/shemminger/iproute2.git;a=summary git repo] or download the [http://kernel.org/pub/linux/utils/net/iproute2/ tarball] to compile it manually. In order to tell to crtools where the proper ip tool is set the <code>CR_IP_TOOL</code> environment variable.+ + + − === Dump and restore ===+ − − Restoring is symmetrical. The way LXC container works imposes some more requirements on crtools usage. − * In order to properly isolate container from unwanted networking communication during checkpoint/restore you should provide a script for locking/unlocking the container network (see below)+ − * When restoring a container with veth device you may specify a name for the host-side veth device − * In order to checkpoint and restore alive TCP connections you should use the <code>--tcp-established</code> option − Typically a container dump command will look like+ − <pre> − crtools dump − --tcp-established # allow for TCP connections dump − -n net -n mnt -n ipc -n pid # dump all the namespaces container uses − --action-script "net-script.sh" # use net-script.sh to lock/unlock networking − -D dump/ -o dump.log # set images dir to dump/ and put logs into dump.log file − -t ${init-pid} # start dumping from task ${init-pid}. It should be container's init − </pre> − and restore command like − <pre> − crtools restore − --tcp-established − -n net -n mnt -n ipc -n pid − --action-script "net-script.sh" − --veth-pair eth0=${veth-name} # when restoring a veth link use ${veth-name} for host-side device end − --root ${path} # path to container root. It should be a root of a (bind)mount − -D data/ -o restore.log − -t ${init-pid} − </pre> − We also find it useful to use the <code>--restore-detached</code> option for restore to make contianer reparent to init rather than hanging on a crtools process launched from shell. Another useful option is the <code>--pidfile</code> one -- you will be able to find out the host-side pid of a container init after restore.+ − Also note, that there's a BUG in how LXC prepares the /dev filesystem for a container which sometimes makes it impossible to dump and container. The <code>--evasive-devices</code> option can help.+ + − More details on the option mentioned can be found in [[Usage]] and [[Advanced usage]] pages.+ − + − === Example === − We have [http://git.criu.org/?p=crtools.git;a=tree;f=test/app-emu/lxc;hb=HEAD an application test] for dumping/restoring an LXC Container. You may look at it for better understanding how to dump and restore your container with crtools. − − This test contains two scripts: − ;[http://git.criu.org/?p=crtools.git;a=blob;f=test/app-emu/lxc/run.sh;hb=HEAD run.sh] − :This is the main script, which executes ''crtools'' two times for dumping and restoring CT. It contains a working commands for dumping and restoring a container. − − ;[http://git.criu.org/?p=crtools.git;a=blob;f=test/app-emu/lxc/network-script.sh;hb=HEAD network-script.sh] − : This one is used to lock and unlock CT's network as described above.
→Troubleshooting: to level2
== Requirements ==
You should have built and installed a recent (>= 1.3.1) version of CRIU.
=== Requirements ===
== Checkpointing and restoring a container ==
LXC upstream has begun to integrate checkpoint/restore support through the lxc-checkpoint tool. This functionality has been in the recent released version of LXC---LXC 1.1.0 , you can install the LXC 1.1.0 or you can check out the development version on Ubuntu by doing:
<source lang="bash">
sudo add-apt-repository ppa:ubuntu-lxc/daily
sudo apt-get update
sudo apt-get install lxc
</source>
Next, create a container:
<source lang="bash">
sudo lxc-create -t ubuntu -n u1 -- -r trusty -a amd64
</source>
And add the following lines (as above) to its config:
=== Create and start a container ===
<source lang="bash">
cat | sudo tee -a /var/lib/lxc/u1/config << EOF
# hax for criu
lxc.console = none
lxc.tty = 0
lxc.cgroup.devices.deny = c 5:1 rwm
EOF
</source>
Finally, start, and checkpoint the container:
<source lang="bash">
sudo lxc-start -n u1
sleep 5s # let the container get to a more interesting state
sudo lxc-checkpoint -s -D /tmp/checkpoint -n u1
</source>
At this point, the container's state is stored in /tmp/checkpoint, and the filesystem is in /var/lib/lxc/u1/rootfs. You can restore the container by doing:
== Checkpoint and restore an LXC Container ==
<source lang="bash">
sudo lxc-checkpoint -r -D /tmp/checkpoint -n u1
</source>
And then, get your container's IP and ssh in:
<source lang="bash">
ssh ubuntu@$(sudo lxc-info -i -H -n u1)
</source>
== Troubleshooting ==
=== Error (mount.c:805): fusectl isn't empty: 8388625 ===
Dumping of fuse filesystems is currently not supported. Empty the container's <code>/sys/fs/fuse/connections</code> and try again.
Dumping and restoring an LXC contianer means -- dumping a subtree of processes starting from container init plus all kinds of namespaces.
=== Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing ===
CRIU doesn't yet support shared mountpoints as LXC does; make sure your rootfs is on a non-shared mount.
== External links ==
* [https://www.youtube.com/watch?v=a9T2gcnQg2k&feature=youtu.be&t=18m8s The New New Thing: Turning Docker Tech into a Full Speed Hypervisor] - Talk of Tycho Andersen with demo of migration LXC container with Doom inside
* [https://github.com/tych0/presentations/blob/master/ods2014.md Demo script]
[[Category: HOWTO]]
[[Category: Live migration]]