Juju 2.1 and CentOS

In the Juju 2.1 release, I made a couple of small changes to better support CentOS servers.

The first change was to support “manual provisioning” of CentOS machines. Manual provisioning is when you point Juju at a machine, and Juju connects to the machine over SSH and sets it up with a Juju agent. To do this, Juju needs to run a small shell script to discover the OS version and hardware characteristics of the machine. With a minor change to that script, you can now manually provision CentOS machines.

The second change is to support CentOS LXD images. A small change was needed in the Juju code to support the “centos7” OS version, and alter the way we handle local LXD image aliases. If an image exists locally with the expected alias (e.g. “juju/centos7/amd64”), then we’ll use that and skip looking in the remote image sources. This also improves container startup time when you live in a faraway land like me. Altering Juju is not quite enough though, as there are no existing CentOS images that Juju can use.

Juju (mostly) requires cloud-init to be present on the machines it starts, so that it can inject Juju-specific configuration and scripts to run on startup. Unforunately, there are no CentOS LXD images that have cloud-init already. To work around this, I wrote a standalone Go program to transform the linuxcontainers.org CentOS image: github.com/axw/juju-lxd-centos-image-builder. Eventually we hope to have pre-canned CentOS LXD images available to Juju, but for now you can use this program to prepare an image for Juju. Run it from the LXD host, and Juju will be able to use the resulting image.

Posted February 23, 2017. Tags: juju, lxd.