Linux Containers and the Future Cloud

LXC Container Management

First, you should verify that your host supports LXC by running lxc-checkconfig. If everything is okay, you can create a container by using one of several ready-made templates for creating containers. In lxc-0.9, there are 11 such templates, mostly for popular Linux distributions. You easily can tailor these templates according to your requirements, if needed. So, for example, you can create a Fedora container called fedoraCT with:


lxc-create -t fedora -n fedoraCT

The container will be created by default under /var/lib/lxc/fedoraCT. You can set a different path for the generated container by adding the --lxcpath PATH option.

The -t option specifies the name of the template to be used, (fedora in this case), and the -n option specifies the name of the container (fedoraCT in this case). Note that you also can create containers of other distributions on Fedora, for example of Ubuntu (you need the debootstrap package for it). Not all combinations are guaranteed to work.

You can pass parameters to lxc-create after adding --. For example, you can create an older release of several distributions with the -R or -r option, depending on the distribution template. To create an older Fedora container on a host running Fedora 20, you can run:


lxc-create -t fedora -n fedora19 -- -R 19

You can remove the installation of an LXC container from the filesystem with:


lxc-destroy -n fedoraCT

For most templates, when a template is used for the first time, several required package files are downloaded and cached on disk under /var/cache/lxc. These files are used when creating a new container with that same template, and as a result, creating a container that uses the same template will be faster next time.

You can start the container you created with:


lxc-start -n fedoraCT

And stop it with:


lxc-stop -n fedoraCT

The signal used by lxc-stop is SIGPWR by default. In order to use SIGKILL in the earlier example, you should add -k to lxc-stop:


lxc-stop -n fedoraCT -k

You also can start a container as a dæmon by adding -d, and then log on into it with lxc-console, like this:


lxc-start -d -n fedoraCT
lxc-console -n fedoraCT

The first lxc-console that you run for a given container will connect you to tty1. If tty1 already is in use (because that's the second lxc-console that you run for that container), you will be connected to tty2 and so on. Keep in mind that the maximum number of ttys is configured by the lxc.tty entry in the container configuration file.

You can make a snapshot of a non-running container with:


lxc-snapshot -n fedoraCT

This will create a snapshot under /var/lib/lxcsnaps/fedoraCT. The first snapshot you create will be called snap0; the second one will be called snap1 and so on. You can time-restore the snapshot at a later time with the -r option—for example:


lxc-snapshot -n fedoraCT -r snap0 restoredFdoraCT

You can list the snapshots with:


lxc-snapshot -L -n fedoraCT

You can display the running containers by running:


lxc-ls --active

Managing containers also can be done via scripts, using scripting languages. For example, this short Python script starts the fedoraCT container:


#!/usr/bin/python3

import lxc

container = lxc.Container("fedoraCT")
container.start()

Container Configuration

A default config file is generated for every newly created container. This config file is created, by default, in /var/lib/lxc/<containerName>/config, but you can alter that using the --lxcpath PATH option. You can configure various container parameters, such as network parameters, cgroups parameters, device parameters and more. Here are some examples of popular configuration items for the container config file:

  • You can set various cgroups parameters by setting values to the lxc.cgroup.[subsystem name] entries in the config file. The subsystem name is the name of the cgroup controller. For example, configuring the maximum memory a container can use to be 256MB is done by setting lxc.cgroup.memory.limit_in_bytes to be 256MB.

  • You can configure the container hostname by setting lxc.utsname.

  • There are five types of network interfaces that you can set with the lxc.network.type parameter: empty, veth, vlan, macvlan and phys. Using veth is very common in order to be able to connect a container to the outside world. By using phys, you can move network interfaces from the host network namespace to the container network namespace.

  • There are features that can be used for hardening the security of LXC containers. You can avoid some specified system calls from being called from within a container by setting a secure computing mode, or seccomp, policy with the lxc.seccomp entry in the configuration file. You also can remove capabilities from a container with the lxc.cap.drop entry. For example, setting lxc.cap.drop = sys_module will create a container without the CAP_SYS_MDOULE capability. Trying to run insmod from inside this container will fail. You also can define Apparmor and SELinux profiles for your container. You can find examples in the LXC README and in man 5 lxc.conf.

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