Systemd's system extensions (sysexts) provide a mechanism to extend host's content while preserving the safety guarantees around updates. Some image based OS like Flatcar, Fedora CoreOS or Atomic Desktops are leveraging sysext images to provide container runtimes. In this tutorial, Mathieu will give you the fundamentals of sysexts to help you building, running and updating your very first sysext images. From simple sysext-images like Containerd to more complex ones: learn how to securely extend image based systems.