Fedora CoreOS Frequently Asked Questions
Fedora CoreOS is an automatically updating, minimal, monolithic, container-focused operating system, designed for clusters but also operable standalone, optimized for Kubernetes but also great without it. It aims to combine the best of both CoreOS Container Linux and Fedora Atomic Host, integrating technology like Ignition from Container Linux with rpm-ostree and SELinux hardening from Project Atomic. Its goal is to provide the best container host to run containerized workloads securely and at scale.
Fedora CoreOS is a freely available, community distribution that is the upstream basis for Red Hat CoreOS. While Fedora CoreOS will embrace a variety of containerized use cases, Red Hat CoreOS will provide a focused immutable host for OpenShift, released and life-cycled in tandem with the platform.
Fedora CoreOS will eventually become the successor to Container Linux. The Container Linux project has a large installed base - it is a top priority to not disrupt that. The project will continue to be supported at least throughout 2019, allowing users ample time to migrate and provide feedback. Existing Container Linux users can be confident that support will continue while the next version is being created in parallel, in a non-disruptive way.
Does Fedora CoreOS replace Fedora Atomic Host? What happens to Fedora Atomic Host and CentOS Atomic Host?
Fedora CoreOS will also become the successor to Fedora Atomic Host. The current plan is for Fedora Atomic Host to have at least a 29 version and 6 months of lifecycle.
CentOS Atomic Host will continue producing downstream rebuilds of RHEL Atomic Host and will align with the end-of-life. The Fedora CoreOS project will be the consolidation point for the community distributions. Users are encouraged to move there in the future.
Project Atomic is an umbrella project consisting of two flavors of Atomic Host (Fedora and CentOS) as well as various other container-related projects. Project Atomic as a project name will be sunset by the end of 2018 with a stronger individual focus on its successful projects such as Buildah and Cockpit. This merges the community side of the operating system more effectively with Fedora and allows for a clearer communication for other community-supported projects, specifically the well-adopted #nobigfatdaemons approach of Buildah and the versatile GUI server manager Cockpit.
We have the following new communication channels around Fedora CoreOS:
The CoreOS Update Philosophy stays as important to us as always. Yes, Fedora CoreOS comes with automatic updates and regular releases. Multiple update channels are provided catering to different users' needs. It will introduce a new node-update service based on rpm-ostree technologies, with a server component that can be optionally self-hosted. Failures that prevent an update from booting will automatically be reverted.
Fedora CoreOS will be provisioned with Ignition. However, existing Ignition configurations may require changes, as the OS configuration will be different from Container Linux. Existing cloud-init configurations are not supported and will need to be migrated into their Ignition equivalent.
Migration will be accomplished by re-provisioning the machine with Fedora CoreOS. We will provide documentation to make this easier, as well as tooling to help convert existing cloud-configs and Ignition configs for use on Fedora CoreOS.
As with Container Linux, the best practice will be re-provisioning, due to the cloud-init/Ignition transition at least. Since Fedora CoreOS will be using rpm-ostree technology, it may be possible to rebase from Fedora Atomic Host to Fedora CoreOS, but it will not be recommended. It will be preferable to gain experience deploying systems using Ignition so that they can be re-provisioned easily if needed. This will all be part of a "migrating from Fedora Atomic Host" guide which will be published soon.
Fedora CoreOS includes the Docker, podman, and CRI-O container runtimes by default. Based on community engagement and support this list could change over time.
Fedora CoreOS is expected to run on at least
and bare-metal systems if installed to disk or network-booted.
Yes. However, we envision Fedora CoreOS as not including a specific container orchestrator (or version of Kubernetes) by default — just like Container Linux and Atomic Host. We will work with the upstream Kubernetes community on tools (e.g. kubeadm) and best practices for installing Kubernetes on Fedora CoreOS.
On Fedora CoreOS, containers are the way to install and configure any software not provided by the base operating system. The package layering mechanism provided by rpm-ostree will continue to exist for use in debugging a Fedora CoreOS machine, but we strongly discourage its use in production. For more about this, please refer to upcoming documentation.
How do I coordinate cluster-wide OS updates? Is locksmith or the Container Linux Update Operator available for Fedora CoreOS?
We have ported the Container Linux Update Operator to use rpm-ostree in the upstream repo. If you are using Fedora CoreOS outside of a Kubernetes cluster, you will be able to use upcoming tools to coordinate updates and reboots.