Difference between revisions of "LXC"

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]

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
Demo script

@@ Line 1: / Line 1: @@
-=Prepare a Linux Container=
+== Requirements ==
-==Requirements==
-* A console should be disabled (lxc.console = none)
-* udev should not run inside containers ($ mv /sbin/udevd{,.bcp})
-== Preparing a host environment ==
+You should have built and installed a recent (>= 1.3.1) version of CRIU.
-* Mount cgroupfs
+== Checkpointing and restoring a container ==
- $ 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.
- curl http://download.openvz.org/template/precreated/centos-6-x86_64.tar.gz | tar -xz -C test-lxc
-* Create config files
+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:
- $ cat ~/test-lxc.conf
+<source lang="bash">
- lxc.console=none
+sudo add-apt-repository ppa:ubuntu-lxc/daily
- lxc.utsname = test-lxc
+sudo apt-get update
- lxc.network.type = veth
+sudo apt-get install lxc
- lxc.network.flags = up
+</source>
- 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
+Next, create a 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
+<source lang="bash">
-  $ lxc-create -n test-lxc -f test-lxc.conf
+  sudo lxc-create -t ubuntu -n u1 -- -r trusty -a amd64
+</source>
-* Start the container
+And add the following lines (as above) to its config:
- $ mount --bind test-lxc test-lxc-root/
- $ lxc-start -n test-lxc
-= Checkpoint and restore an LXC Container =
+<source lang="bash">
-== Preparations ==
+cat | sudo tee -a /var/lib/lxc/u1/config << EOF
-You only need to [[Installation | install]] the crtools.
+# 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
+</source>
-== Dump and restore ==
+Finally, start, and checkpoint the container:
-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.
-* You need to use the <code>--evasive-devices</code> option to handle <code>/dev/log</code> users (there's a bug in LXC code)
+<source lang="bash">
-* 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)
+sudo lxc-start -n u1
-* When restoring a container with veth device you may specify a name for the host-side veth device
+sleep 5s  # let the container get to a more interesting state
-* In order to checkpoint and restore alive TCP connections you should use the <code>--tcp-established</code> option
+sudo lxc-checkpoint -s -D /tmp/checkpoint -n u1
+</source>
-Typically a container dump command will look like
+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:
-<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 ${init-pid}
-</pre>
-We also find it useful to use the <code>--restore-detached</code> option for restore to make contianer reparent to init rather than hanging on a crtools process launched from shell. Another useful option is the <code>--pidfile</code> one -- you will be able to find out the host-side pid of a container init after restore.
+<source lang="bash">
+sudo lxc-checkpoint -r -D /tmp/checkpoint -n u1
+</source>
-Also note, that there's a BUG in how LXC prepares the /dev filesystem for a container which sometimes makes it impossible to dump and container. The <code>--evasive-devices</code> option can help.
+And then, get your container's IP and ssh in:
-More details on the option mentioned can be found in [[Usage]] and [[Advanced usage]] pages.
+<source lang="bash">
+ssh ubuntu@$(sudo lxc-info -i -H -n u1)
+</source>
-== Example ==
+== Troubleshooting ==
-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.
+=== Error (mount.c:805): fusectl isn't empty: 8388625 ===
-This test contains two scripts:
+Dumping of fuse filesystems is currently not supported. Empty the container's <code>/sys/fs/fuse/connections</code> and try again.
-;[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]
+=== Error (mount.c:517): Mount 58 (master_id: 12 shared_id: 0) has unreachable sharing ===
-: This one is used to lock and unlock CT's network as described above.
+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]]