Dockerlite: lightweight Linux virtualization with BTRFS and LXC

Dockerlite lets you run Linux apps in lightweight, isolated environments, using LXC (Linux Containers). It is inspired by Docker and it actually reimplements some of its most basic features.

Using BTRFS snapshots, dockerlite can save the state of a given environment in a frozen "image", and later, create more environments ("containers") out of that image.

It was inspired by Docker, and aims at being a sandbox to experiment new concepts linked with the Docker project.

It is not a replacement for Docker. It is missing (at least) the following features:

• registry protocol (i.e. it is not possible to push/pull images)
• index protocol (i.e. it is not possible to search images)
• REST API (i.e. the only way to use Dockerlite is through the CLI)
• Dockerfile (i.e. you cannot dockerlite build)
• and many more.

Its main feature is HACKABILITY: 9000 since it's shell, and everybody including your dog can write shell scripts, right?

Installation

See INSTALL.md.

How to use it

See MANUAL.md.

What's "lightweight" virtualization?

A Linux container looks like a virtual machine: it has its own network stack, IP address, process space; it is isolated from its sibling containers (it can't see them and can't be seen by them). However, it runs on top of the same kernel as its host. This means that if your machine runs Linux 3.8, all containers on this machine will also run Linux 3.8. You cannot run another kernel (or another OS) within a container. Of course, you could run a full virtual machine within qemu or kvm within a container, but that's a different story!

Where the name dockerlite comes from?

dockerlite is a "light" version of Docker. The latter has similar features, but with the following major differences:

• Docker is written in Go, while dockerlite is a Posix Shell script;
• Docker storage relies on AUFS, while dockerlite uses BTRFS;
• Docker runs as a background daemon, and is operated through a CLI client, while dockerlite does not run in the background.

Docker also has some extra features to store images in 3rd party services.

Why dockerlite?

dockerlite initially targetted the following goals:

• demonstrate that the core features provided by Docker can be easily reimplemented with simple, easy-to-audit, shell scripts;
• provide an alternative implementation to Docker, with a strong emphasis on "hackability", i.e. a lightweight testbed for new features which can be more cumbersome to implement in a full-blown Go project;
• evaluate BTRFS in the context of Docker.

The first goal is loosely defined, depending on what you want to put in the "core features" of Docker. If you just want to create images and containers, then "misson complete". If you want to push/pull and use a REST API, it's a long shot.

The other goals were met. Dockerlite confirmed that BTRFS was an acceptable option and that there were no unplanned side-effect or shotstopper preventing its use for Docker containers. It also served to evaluate different ways to setup the containers networking stack.

License

Apache 2 License

For JSON.sh license, see https://github.com/dominictarr/JSON.sh