Difference between revisions of "LXC"

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=Prepare a Linux Container=
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== Requirements ==
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==Requirements==
 
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* A console should be disabled (lxc.console = none)
 
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* udev should not run inside containers ($ mv /sbin/udevd{,.bcp})
 
  
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== Preparing a host environment ==
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You should have built and installed a recent (>= 1.3.1) version of CRIU.
  
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* Mount cgroupfs
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== Checkpointing and restoring a container ==
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$ mount -t cgroup c /cgroup
 
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* Create a network bridge
 
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# cat /etc/sysconfig/network-scripts/ifcfg-br0
 
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DEVICE=br0
 
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TYPE=Bridge
 
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BOOTPROTO=dhcp
 
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ONBOOT=yes
 
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DELAY=5
 
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NM_CONTROLLED=n
 
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$ cat /etc/sysconfig/network-scripts/ifcfg-eth0
 
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DEVICE="eth0"
 
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NM_CONTROLLED="no"
 
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ONBOOT="yes"
 
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BRIDGE=br0
 
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==Create and start a container==  
 
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* Download an OpenVZ template and extract it.
 
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curl http://download.openvz.org/template/precreated/centos-6-x86_64.tar.gz | tar -xz -C test-lxc
 
  
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* Create config files
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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:
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$ cat ~/test-lxc.conf
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<source lang="bash">
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lxc.console=none
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sudo add-apt-repository ppa:ubuntu-lxc/daily
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lxc.utsname = test-lxc
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sudo apt-get update
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lxc.network.type = veth
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sudo apt-get install lxc
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lxc.network.flags = up
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</source>
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lxc.network.link = br0
 
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lxc.network.name = eth0
 
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lxc.mount = /root/test-lxc/etc/fstab
 
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lxc.rootfs = /root/test-lxc-root/
 
  
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$ cat /root/test-lxc/etc/fstab
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Next, create a container:
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none /root/test-lxc-root/dev/pts devpts defaults 0 0
 
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none /root/test-lxc-root/proc    proc  defaults 0 0
 
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none /root/test-lxc-root/sys    sysfs  defaults 0 0
 
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none /root/test-lxc-root/dev/shm tmpfs  defaults 0 0
 
  
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* Register the container
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<source lang="bash">
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  $ lxc-create -n test-lxc -f test-lxc.conf
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  sudo lxc-create -t ubuntu -n u1 -- -r trusty -a amd64
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</source>
  
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* Start the container
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And add the following lines (as above) to its config:
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$ mount --bind test-lxc test-lxc-root/
 
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$ lxc-start -n test-lxc
 
  
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= Checkpoint and restore an LXC Container =
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<source lang="bash">
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== Preparations ==
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cat | sudo tee -a /var/lib/lxc/u1/config << EOF
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You only need to [[Installation | install]] the crtools.
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# hax for criu
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lxc.console = none
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lxc.tty = 0
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lxc.cgroup.devices.deny = c 5:1 rwm
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EOF
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</source>
  
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== Dump and restore ==
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Finally, start, and checkpoint the container:
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Dumping and restoring an LXC contianer means -- dumping a subtree of processes starting from container init plus all kinds of namespaces.
 
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Restoring is symmetrical. The way LXC container works imposes some more requirements on crtools usage.
 
  
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* You need to use the <code>--evasive-devices</code> option to handle <code>/dev/log</code> users (there's a bug in LXC code)
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<source lang="bash">
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* 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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sudo lxc-start -n u1
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* When restoring a container with veth device you may specify a name for the host-side veth device
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sleep 5s  # let the container get to a more interesting state
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* In order to checkpoint and restore alive TCP connections you should use the <code>--tcp-established</code> option
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sudo lxc-checkpoint -s -D /tmp/checkpoint -n u1
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</source>
  
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Typically a container dump command will look like
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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:
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<pre>
 
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crtools dump
 
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    --evasive-devices                # handle /dev/log usage bug
 
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    --tcp-established                # allow for TCP connections dump
 
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    -n net -n mnt -n ipc -n pid      # dump all the namespaces container uses
 
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    --action-script "net-script.sh"  # use net-script.sh to lock/unlock networking
 
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    -D dump/ -o dump.log            # set images dir to dump/ and put logs into dump.log file
 
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    -t ${init-pid}                  # start dumping from task ${init-pid}. It should be container's init
 
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</pre>
 
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and restore command like
 
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<pre>
 
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crtools restore
 
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  --evasive-devices
 
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  --tcp-established
 
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  -n net -n mnt -n ipc -n pid
 
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  --action-script "net-script.sh"
 
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  --veth-pair eth0=${veth-name}    # when restoring a veth link use ${veth-name} for host-side device end
 
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  --root ${path}                    # path to container root. It should be a root of a (bind)mount
 
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  -D data/ -o restore.log
 
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  -t ${init-pid}
 
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</pre>
 
  
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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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<source lang="bash">
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sudo lxc-checkpoint -r -D /tmp/checkpoint -n u1
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</source>
  
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== Example ==
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And then, get your container's IP and ssh in:
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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.
 
  
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This test contains two scripts:
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<source lang="bash">
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;[http://git.criu.org/?p=crtools.git;a=blob;f=test/app-emu/lxc/run.sh;hb=HEAD run.sh]
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ssh ubuntu@$(sudo lxc-info -i -H -n u1)
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: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.
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</source>
  
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;[http://git.criu.org/?p=crtools.git;a=blob;f=test/app-emu/lxc/network-script.sh;hb=HEAD network-script.sh]
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== Troubleshooting ==
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: This one is used to lock and unlock CT's network as described above.
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 +
=== Error (mount.c:805): fusectl isn't empty: 8388625 ===
 +
 
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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.
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=== Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing ===
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CRIU doesn't yet support shared mountpoints as LXC does; make sure your rootfs is on a non-shared mount.
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== External links ==
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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]
 +
 
 +
[[Category: HOWTO]]
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[[Category: Live migration]]

Latest revision as of 19:20, 21 September 2016

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 = 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]

Retrieved from "https://criu.org/index.php?title=LXC&oldid=3545"