Docker in LXD

Since the very early days of upstream Linux containers – around 2006 – we’ve been distinguishing between ‘application’ and ‘system’ containers. (The definition of application containers has changed a bit, and their use case has changed a *lot*, but the general gist remains the same).

A few years ago I would get regular – daily! – queries by lots of people asking what I thought of Docker. Some asked because, as one of the early people involved in kernel container functionality, I’d be interested. Others did so because I had been working with http://linuxcontainers.org/lxc, a particular container administration suite, and thought I’d feel competitive. However, as we’ve said for a long time, Docker is a great tool for application containers and application container purposes. From a LXC/LXD perspective, we’re looking at different use cases. One of those is hosting containers in which to run Docker 🙂

And, in Ubuntu 16.04, you can easily do so. (The Docker patches to enable this are on their way upstream.) To run Docker inside a container, the container must have a few properties. These are conferred by the ‘docker’ profile. The docker profile does not include a network interface, so you’ll want to create a container with both the default and docker profiles:

lxc launch ubuntu-daily:xenial docker1 -p default -p docker

Now, enter the container and install the docker.io package:

lxc exec docker1 — apt update
lxc exec docker1 — apt install docker.io
lxc exec docker1 — docker pull ubuntu
lxc exec docker1 — docker run -it ubuntu bash

et voila, a docker container is running inside your lxd container. By itself this may seem like a novelty. However, when you start deploying the lxd hosts with openstack nova-lxd plugin or juju-lxd, the possibilities are endless.

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8 Responses to Docker in LXD

  1. Michele says:

    Are the Docker patches already upstream or we still have to wait? Were can we track progress for this inclusion?

  2. morswin90 says:

    Hi,
    I’m using LXD with a separate zfs partition on a host. I would like to start a container for nested docker containers. Which storage driver should I use in docker configuration?

    Regards,
    Matthew

    • s3hh says:

      Hi,

      not quite sure, and it depends what distro/release you’re using, but I think using overlay (on a ubuntu xenial or later) would work best.

      • morswin90 says:

        Hello,
        I use Ubuntu 16.10 and using overlay I got errors:
        level=error msg=”‘overlay2’ is not supported over zfs”
        level=fatal msg=”Error starting daemon: error initializing graphdriver: backing file system is unsupported for this graph driver”

        So I decided to use ZFS also as docker storage engine (but different pool). Shortly: How to enforce linux to let a nonroot user mount ZFS in legacy mode (using mount -F zfs or mount.zfs)?

        I use LXD with ZFS storage engine and on the guest machine I am trying to run docker also with ZFS storage engine (but on different pool). The problem is that a root user on LXD guest machine is not the same as root on host (I use LXD in unprivileged mode). Therefore I need to give a change to the nonroot user to mount ZFS – docker does it in legacy mode.

        Regards,
        Matthew

  3. s3hh says:

    Oh yeah, I forgot about that. I had run into that once, but never dove deeper to see whether overlay over zfs really is a problem or not. You might ask on freenode#ubuntu-kernel. If there’s not a good reason then docker could be patched to drop that check.

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