8
edits
Changes
Jump to navigation
Jump to search
Line 1:
Line 1: − This article describes how to perform checkpoint-restore for an LXC container. There are two ways to do this, the first part of the article describes how to dump a container with LXC directly, and the second part describes how to do it using tools under development in LXC upstream.+ − == 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 − − === Create and start a container === − * 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/ − lxc.console = none − lxc.tty = 0 − − $ 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 − − == Checkpoint and restore an LXC Container == − − === Preparations === − − You not only need to [[Installation | install]] the criu, 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 criu where the proper ip tool is set the <code>CR_IP_TOOL</code> environment variable. − − === Dump and restore === − Dumping and restoring an LXC contianer means -- dumping a subtree of processes starting from container init plus all kinds of namespaces. − Restoring is symmetrical. The way LXC container works imposes some more requirements on criu 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> − criu dump − --tcp-established # allow for TCP connections dump − --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 ${init-pid}. It should be container's init − </pre> − and restore command like − <pre> − criu restore − --tcp-established − --action-script "net-script.sh" − --veth-pair eth0=${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 criu 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 criu. − − 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 ''criu'' 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. − − ===FAQ=== − * CRIU supports restricted number of file systems: proc, sysfs, devtmpfs, tmpfs, binfmt_misc. All unsupported file systems must be umounted or handled by plugins. − Error (mount.c:737): FS mnt /sys/fs/pstore dev 0x18 root / unsupported − − * /dev/console isn't supported yet. You can try to remove the "lxc.cgroup.devices.allow = c 5:1 rwm" from a CT config. − Error (tty.c:203): tty: Can't obtain ptmx index: Inappropriate ioctl for device − − * Netlink sockets with pending messages are not supported. You can try again later. − Error (sk-netlink.c:77): The socket has data to read − − * Quite often CRIU can complain about [[external bind mounts]] like this − ... doesn't have a proper root mount − consider using the <code>--ext-mount-map</code> option − − == Using LXC Upstream tools == Line 168:
Line 49: + + + + + + + + + +
no edit summary
== 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. Although this functionality is not in any released version of LXC yet, you can check out the development version on Ubuntu by doing:
LXC upstream has begun to integrate checkpoint/restore support through the lxc-checkpoint tool. Although this functionality is not in any released version of LXC yet, you can check out the development version on Ubuntu by doing:
ssh ubuntu@$(sudo lxc-info -i -H -n u1)
ssh ubuntu@$(sudo lxc-info -i -H -n u1)
</pre>
</pre>
===Troubleshooting===
* <pre>Error (sk-netlink.c:77): The socket has data to read</pre>
Netlink sockets with pending messages are not supported. Usually if you run the dump again it will succeed.
* <pre>Error (mount.c:805): fusectl isn't empty: 8388625.</pre>
Dumping of fuse filesystems is currently not supported. Empty the container's /sys/fs/fuse/connections and try again.
* <pre>Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing</pre>
criu doesn't yet support shared mountpoints as lxc does; make sure your rootfs is on a non-shared mount.
[[Category: HOWTO]]
[[Category: HOWTO]]