This talk is about how the Fedora Atomic host is used as a core building block of a container service in a Cloud Infrastructure, private or public. OpenStack/Magnum is a light API service which allows cloud operators to provide container clusters on demand (mostly Kubernetes and Docker Swarm). Firstly, I will describe the architecture of the service, how the Magnum team is doing upstream development, how we add new features and the struggles to be up to date with the newest OS and software releases and how we benefit from the Fedora community. Then, on the downstream side, I'll share the experience of running our container service at CERN with hundreds of Fedora Atomic VMs for more than two years already and experiences from cloud operators in other sites. Finally, I will mention use cases at CERN from CI tools to physics analysis platforms.