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Hey everyone,

This is another update about the development of LXC 3.0.

We are currently in the process of moving various parts of LXC out of the main LXC repository and into separate repositories.

Splitting Out The Language Bindings For Lua And Python 3

The lua language bindings will be moved into the new lua-lxc repository and the Python 3 bindings to the new python3-lxc repository. This is in line with other language bindings like Python 2 (see python2-lxc) that were always kept out of tree.

Splitting Out The Legacy Template Build System

A big portion of the LXC templates will be moved to the new lxc-templates repository. LXC used to maintain simple shell scripts to build container images from for a lot of distributions including CentOS, Fedora, ArchLinux, Ubuntu, Debian and a lot of others. While the shell scripts worked well for a long time they suffered from the problem that they were often different in terms of coding style, the arguments that they expected to be passed, and the features they supported. A lot of things these shells scripts did when creating an image is not needed any more. For example, most distros nowadays provide a custom cloud image suitable for containers and virtual machines or at least provide their own tooling to build clean new images from scratch. Another problem we saw was that security and maintenance for the scripts was not sufficient. This is why we decided to come up with a simple yet elegant replacement for the template system that would still allow users to build custom LXC and LXD container images for the distro of their choice. So the templates will be replaced by distrobuilder as the preferred way to build LXC and LXD images locally. distrobuilder is a project my colleague Thomas is currently working on. It aims to be a very simple Go project focussed on letting you easily build full system container images by either using the official cloud image if one is provided by the distro or by using the respective distro’s recommended tooling (e.g. debootstrap for Debian or pacman for ArchLinux). It aims to be declarative, using the same set of options for all distributions while having extensive validation code to ensure everything that’s downloaded is properly validated.

After this cleanup only four POSIX shell compliant templates will remain in the main LXC repository:

  • lxc-busybox

This is a very minimal template which can be used to setup a busybox container. As long as the busybox binary is found you can always built yourself a very minimal privileged or unprivileged system or application container image; no networking or any other dependencies required. All you need to do is:

lxc-create c3 -t busybox

asciicast

  • lxc-download

This template lets you download pre-built images from our image servers. This is likely what currently most users are using to create unprivileged containers.

  • lxc-local

This is a new template which consumes standard LXC and LXD system container images. A container can be created with:

lxc-create c1 -t local -- --metadata /path/to/meta.tar.xz --fstree /path/to/rootfs.tar.xz

where the --metadata flag needs to point to a file containing the metadata for the container. This is simply the standard meta.tar.xz file that comes with any pre-built LXC container image. The --fstree flag needs to point to a filesystem tree. Creating a container is then just:

asciicast

  • lxc-oci

This is the template which can be used to download and run OCI containers. Using it is as simple as:

lxc-create c2 -t oci -- --url docker://alpine

Here’s another asciicast:

asciicast