rpm-ostree, used together with OStree, is a powerful tool to generate immutable images for .rpm based systems, so why not use it for generating Docker images as well? rpm-ostree already has support for composing a container tree, but the steps to go from an OStree commit to a ready-to-run Docker image involve several manual operations. ostree-docker-builder is a small tool that automates this workflow, taking a JSON package description and producing a tagged Docker image with a minimal Dockerfile.

These are the steps to setup the current website in a Docker container. The setup uses docker-compose to declaratively describe a two-container application: a MySQL 5.5 database and a WordPress frontend. Docker links tie them together so that the web container can reach the database by hostname, without needing to hard-code any IP addresses or manage networking manually. A single docker-compose up command downloads the required images and starts both containers, with port 80 on the host forwarded into the WordPress container.