Immutable Infrastructure with Flatcar Container Linux

<p>Flatcar Container Linux is a minimal base OS to run containers. As a friendly fork of CoreOS Container Linux it continues the project under a new name. The main features are the A/B partitions for automatic updates and rollbacks, and the integration of Ignition for declarative configuration on first boot. Declarative configuration is a key element for managing machines following the principle of Immutable Infrastructure, but causes friction if it means that the whole machine has to be reprovisioned for configuration changes. With Ansible instead of Ignition for the configuration management we can find a compromise by giving up on avoiding configuration drift due to leftovers of old configurations and their side effects. Out of this experience the idea was born to rerun Ignition on configuration changes. While the big hammer method is to reformat the filesystem and losing application data, a more fine-grained solution could exist by clearing only parts of the filesystem. This talk shows how to use Flatcar Container Linux with Terraform, Ignition, and Ansible, and ends with a proof-of-concept demo for Flatcar Container Linux to allow configuration changes through Ignition while avoiding configuration drift.</p>