Difference between revisions of "LXC"

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This article describes how to perform checkpoint-restore for an LXC container.
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== Requirements ==
  
== Preparing a Linux Container ==
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You should have built and installed a recent (>= 1.3.1) version of CRIU.
  
=== Requirements ===
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== Checkpointing and restoring a container ==
  
* A console should be disabled (<code>lxc.console = none</code>)
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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:
* udev should not run inside containers (<code>mv /sbin/udevd{,.bcp}</code>)
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<source lang="bash">
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sudo add-apt-repository ppa:ubuntu-lxc/daily
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sudo apt-get update
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sudo apt-get install lxc
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</source>
  
=== Preparing a host environment ===
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Next, create a container:
  
* Mount cgroupfs
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<source lang="bash">
  $ mount -t cgroup c /cgroup
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  sudo lxc-create -t ubuntu -n u1 -- -r trusty -a amd64
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</source>
  
* Create a network bridge
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And add the following lines (as above) to its config:
# 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 ===
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<source lang="bash">
* Download an OpenVZ template and extract it.
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cat | sudo tee -a /var/lib/lxc/u1/config << EOF
<pre><nowiki>curl http://download.openvz.org/template/precreated/centos-6-x86_64.tar.gz | tar -xz -C test-lxc
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# hax for criu
</nowiki></pre>
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lxc.console.path = none
* Create config files
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lxc.tty.max = 0
$ cat ~/test-lxc.conf
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lxc.cgroup.devices.deny = c 5:1 rwm
lxc.console=none
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# on older lxc comment the above and uncomment the below
lxc.utsname = test-lxc
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# lxc.console = none
lxc.network.type = veth
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# lxc.tty = 0
lxc.network.flags = up
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# lxc.cgroup.devices.deny = c 5:1 rwm
lxc.network.link = br0
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EOF
lxc.network.name = eth0
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</source>
lxc.mount = /root/test-lxc/etc/fstab
 
lxc.rootfs = /root/test-lxc-root/
 
  
$ cat /root/test-lxc/etc/fstab
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Finally, start, and checkpoint the container:
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
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<source lang="bash">
$ lxc-create -n test-lxc -f test-lxc.conf
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sudo lxc-start -n u1
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sleep 5s  # let the container get to a more interesting state
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sudo lxc-checkpoint -s -D /tmp/checkpoint -n u1
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</source>
  
* Start the container
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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:
$ mount --bind test-lxc test-lxc-root/
 
$ lxc-start -n test-lxc
 
  
== Checkpoint and restore an LXC Container ==
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<source lang="bash">
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sudo lxc-checkpoint -r -D /tmp/checkpoint -n u1
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</source>
  
=== Preparations ===
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And then, get your container's IP and ssh in:
  
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.
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<source lang="bash">
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ssh ubuntu@$(sudo lxc-info -i -H -n u1)
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</source>
  
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.
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== Troubleshooting ==
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=== Error (mount.c:805): fusectl isn't empty: 8388625 ===
  
=== Dump and restore ===
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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.
 
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)
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=== Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing ===
* 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
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CRIU doesn't yet support shared mountpoints as LXC does; make sure your rootfs is on a non-shared mount.
<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.
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== External links ==
  
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.
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* [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
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* [https://github.com/tych0/presentations/blob/master/ods2014.md Demo script]
  
More details on the option mentioned can be found in [[Usage]] and [[Advanced usage]] pages.
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[[Category: HOWTO]]
 
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[[Category: Live migration]]
=== 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.
 

Latest revision as of 04:33, 1 July 2024

Requirements[edit]

You should have built and installed a recent (>= 1.3.1) version of CRIU.

Checkpointing and restoring a container[edit]

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:

sudo add-apt-repository ppa:ubuntu-lxc/daily
sudo apt-get update
sudo apt-get install lxc

Next, create a container:

 sudo lxc-create -t ubuntu -n u1 -- -r trusty -a amd64

And add the following lines (as above) to its config:

cat | sudo tee -a /var/lib/lxc/u1/config << EOF
# hax for criu
lxc.console.path = none
lxc.tty.max = 0
lxc.cgroup.devices.deny = c 5:1 rwm
# on older lxc comment the above and uncomment the below
# lxc.console = none
# lxc.tty = 0
# lxc.cgroup.devices.deny = c 5:1 rwm
EOF

Finally, start, and checkpoint the container:

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

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:

sudo lxc-checkpoint -r -D /tmp/checkpoint -n u1

And then, get your container's IP and ssh in:

ssh ubuntu@$(sudo lxc-info -i -H -n u1)

Troubleshooting[edit]

Error (mount.c:805): fusectl isn't empty: 8388625[edit]

Dumping of fuse filesystems is currently not supported. Empty the container's /sys/fs/fuse/connections and try again.

Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing[edit]

CRIU doesn't yet support shared mountpoints as LXC does; make sure your rootfs is on a non-shared mount.

External links[edit]