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LXC Fun
Linux Containers, or LXC, is a Linux feature that allows Linux to run one or more isolated virtual systems (with their own network interfaces, process namespace, user namespace, and power state) using a single Linux kernel on a single server. To learn more take a look at the LXC article.
In this Howto you will be shown how to create containers, how to start, stop, freeze and unfreeze them and also some more fun parts like snapshoting and clonig. To have all this working you will have to have your lxc store (/var/lib/lxc/ and /var/lib/lxcsnaps) to be on a btrfs filesystem.
Creating containers
Creating containers is quite easy using lxc-templates. They are located in the /usr/share/lxc/templates directory. You can find there many distributions like archlinux, centos, debian, fedora, opensuse, ubuntu, gentoo and some more. There is also an inofficial funtoo template that can be found at https://github.com/golodhrim/lxc-funtoo/blob/master/lxc-funtoo. The script creates funtoo container, however I was not able to use it with lxc-create script from the lxc utils. You have to run it as a stand-alone script.
So how do you create other containers? I am going to use a debian container for this howto. You will have to emerge debootstrap.
root # emerge -av debootstrap * IMPORTANT: 8 news items need reading for repository 'gentoo'. * Use eselect news to read news items. These are the packages that would be merged, in order: Calculating dependencies... done! [ebuild N ] dev-perl/TimeDate-2.300.0 31 kB [ebuild N ] app-arch/dpkg-1.17.10 USE="bzip2 lzma nls unicode update-alternatives zlib -dselect {-test}" 4,100 kB [ebuild N ] dev-util/debootstrap-1.0.59 96 kB Total: 3 packages (3 new), Size of downloads: 4,226 kB Would you like to merge these packages? [Yes/No]
After installing debootstrap, you can create your debian container using:
root # lxc-create -B btrfs -n vm1 -t debian debootstrap is /usr/bin/debootstrap Checking cache download in /var/cache/lxc/debian/rootfs-wheezy-armhf ... Copying rootfs to /var/lib/lxc/vm1/rootfs...Generating locales (this might take a while)... en_US.UTF-8... done Generation complete. update-rc.d: using dependency based boot sequencing update-rc.d: using dependency based boot sequencing update-rc.d: using dependency based boot sequencing update-rc.d: using dependency based boot sequencing Creating SSH2 RSA key; this may take some time ... Creating SSH2 DSA key; this may take some time ... Creating SSH2 ECDSA key; this may take some time ... invoke-rc.d: policy-rc.d denied execution of restart. Timezone in container is not configured. Adjust it manually. Root password is 'root', please change !
We will see that the lxc-create command created a subvolume on BTRFS backing file system (-B switch took care of this).
root # btrfs sub list / ---- snip ---- ID 1143 gen 437 top level 5 path var/lib/lxc/vm1/rootfs ---- snip ----
Now you are ready to do all the fun stuff with your LXCs.
Starting/stoping containers
To start a previously created container use the lxc utils:
root # lxc-start -n vm1 -d root # lxc-info -n vm1 Name: vm1 State: RUNNING PID: 29742 IP: 172.16.65.234 CPU use: 2.92 seconds BlkIO use: 260.00 KiB Memory use: 2.99 MiB KMem use: 0 bytes Link: vethTN4NGU TX bytes: 2.33 KiB RX bytes: 39.54 KiB Total bytes: 41.87 KiB root # lxc-attach -n vm1 root # root@vm1:~# root # root@vm1:~# exit root # lxc-stop -n vm1 Name: vm1 State: STOPPED
Freezing/unfreezing containers
The command lxc-freeze freezes all the processes running inside the container. The processes will be blocked until they are explicitly thawed by the lxc-unfreeze command. To freeze a previously started container use the lxc utils:
root # lxc-freeze -n vm1 root # lxc-info -n vm1 Name: vm1 State: FROZEN PID: 6817 IP: 172.16.65.234 CPU use: 2.78 seconds BlkIO use: 0 bytes Memory use: 2.47 MiB KMem use: 0 bytes Link: veth7E1J8R TX bytes: 1.45 KiB RX bytes: 3.85 KiB Total bytes: 5.31 KiB root # lxc-unfreeze -n vm1 root # lxc-info -n vm1 Name: vm1 State: RUNNING PID: 6817 IP: 172.16.65.234 CPU use: 2.78 seconds BlkIO use: 0 bytes Memory use: 2.47 MiB KMem use: 0 bytes Link: veth7E1J8R TX bytes: 1.58 KiB RX bytes: 11.13 KiB Total bytes: 12.71 KiB
Clones and snapshots
Now the really nice features of LXC are snapshots of containers and also creating clones of containers. The command lxc-snapshot creates snapshot under /var/lib/lxcsnaps/ directory, this directory must also reside on a BTRFS filesystem. To snapshot a previously created container use the lxc utils:
root # lxc-snapshot -n vm1 root # lxc-snapshot -L -n vm1 snap0 (/var/lib/lxcsnaps/vm1) 2014:11:15 14:01:18 root # btrfs sub list / --- snip --- ID 1144 gen 448 top level 1136 path var/lib/lxcsnaps/vm1/snap0/rootfs --- snip ---
You can also add comments (using a comment file and -c switch). Lets pretend something didn't go well after an upgrade. No big deal if you remembered to create a snapshot before the upgrade. Now you can restore the container to the last good state.
root # btrfs sub list / --- snip --- ID ''1143'' gen 437 top level 5 path var/lib/lxc/vm1/rootfs ID 1144 gen 448 top level 1136 path var/lib/lxcsnaps/vm1/snap0/rootfs --- snip --- root # lxc-snapshot -L -n vm1 snap0 (/var/lib/lxcsnaps/vm1) 2014:11:15 14:01:18 root # lxc-snapshot -n vm1 -r snap0 root # lxc-snapshot -L -n vm1 snap0 (/var/lib/lxcsnaps/vm1) 2014:11:15 14:01:18 root # btrfs sub list / --- snip --- ID 1144 gen 448 top level 1136 path var/lib/lxcsnaps/vm1/snap0/rootfs ID ''1147'' gen 453 top level 5 path var/lib/lxc/vm1/rootfs --- snip ---
Notice the ID change in btrfs subvolume list command (ID in italics). BTRFS took care of the lxc-snapshot call and restored the snapshot contained in the lxcsnaps/vm1/snap0 directory.
Now clones are containers that are exactly the same as the originating container. So for example you will configure a basic LAMP stack (LXC Apache Mariadb PHP) in one container and want to use different container for different websites. So after doing all the hard work of setting up LAMP you just clone the container using lxc tools.
root # btrfs sub list / --- snip --- ID 1144 gen 448 top level 1136 path var/lib/lxcsnaps/vm1/snap0/rootfs ID 1147 gen 453 top level 5 path var/lib/lxc/vm1/rootfs --- snip --- root # lxc-clone -B btrfs -s vm1 vm2 Created container vm2 as snapshot of vm1 root # btrfs sub list / --- snip --- ID 1144 gen 448 top level 1136 path var/lib/lxcsnaps/vm1/snap0/rootfs ID 1147 gen 455 top level 5 path var/lib/lxc/vm1/rootfs ID 1148 gen 455 top level 5 path var/lib/lxc/vm2/rootfs --- snip ---
Cgroups control
Get or set the value of a state object (for example, 'cpuset.cpus') in the container's cgroup for the corresponding subsystem.
- TODO
Managing devices
- TODO
Monitoring containers
There is a utility lxc-top that shows some basic information about running containers.
root # lxc-top Container CPU CPU CPU BlkIO Mem Name Used Sys User Total Used vm1 3.16 3.00 0.95 13.05 MB 12.70 MB vm2 0.14 0.06 0.10 0.00 372.00 KB vm3 3.39 2.09 1.98 868.00 KB 1.44 MB vm4 3.15 2.01 1.71 0.00 912.00 KB TOTAL (4 ) 9.84 7.16 4.74 13.89 MB 15.40 MB
Web GUI
There are a few web GUIs available for LXC. LXC-Web-Panel is a simple one that does the work good. You can get it from https://github.com/trick77/LXC-Web-Panel (it is a fork of LXC-Web-Panel from https://github.com/lxc-webpanel/LXC-Web-Panel, but supports LXC 1.0). You need flask (dev-python/flask).
- TODO
Summary
LXC is a very powerful virtualization technology, in Linux it is one one many to choose from and that is nice. LXC works off the host's existing vanilla kernel, thanks to functionality called cgroups that was merged into the Linux kernel v2.6.24. This allows operating system-level virtualization, and the ability to run multiple isolated Linux systems in "containers" -- a lightweight version of virtual machines (VM).