I work with Linux containers and container images everyday. I often create new images using
buildah. One day I needed to build a custom image of a virtual machine and in this post you’ll
read how I did it.
In the post GitLab custom executor for Openstack I explained how to create a GitLab executor for Openstack. That executor provisions an Openstack instance for each job and run a job script in it. There is some required software to run jobs:
The user must set up the environment, including the following that must be present in the
Git: Used to clone the repositories.
Git LFS: Pulls any LFS objects that might be in the repository.
GitLab Runner: Used to download/update artifacts and cache.
It means that we need to customize an instance image to include prerequisites.
After some research I found a tool that does exactly what I need.
libguestfs project provides
a set of utilities for accessing and modifying virtual machine disk images.
customize disk images in place. I chose Fedora Cloud image as environment for running GitLab jobs.
The commands to add required software are very simple:
- Download or build
Create a file with a
cat > commands.txt <<EOF install git-core,git-lfs copy-in <path to gitlab-runner binary>:/usr/bin/ chmod 0755:/usr/bin/gitlab-runner selinux-relabel EOF
virt-customize -v -a Fedora-Cloud-Base-35-1.2.x86_64.qcow2 --commands-from-file commands.txt
Pay attention to the
selinux-relabel customization option. This is required for VMs that supports
SELinux. Fedora instance cannot properly start if you modified the image without relabelling.