Red Hat is set to fling a flaming arrow at Red Hat CoreOS Container Linux*, the software firm said as it laid out the details of the end of life timeline for the distro it acquired in January 2018.
CoreOS Container Linux is designed as a lightweight operating system optimised for hosting containers. It supports various cluster architectures, and features an automated update system. The container runtime can be either Docker or rkt (Rocket), an alternative which was developed by the CoreOS team.
When Red Hat acquired CoreOS, it said that Container Linux was "complementary to Red Hat Enterprise Linux, Red Hat Enterprise Linux Atomic Host and Red Hat's integrated container runtime and platform management capabilities." The company also said it would integrate Tectonic, the CoreOS Kubernetes project, and Quay, the CoreOS container registry, with its own OpenShift Kubernetes suite.
Later in 2018, Red Hat said it would cease development of Atomic Host and that a new Red Hat CoreOS, and an associated Fedora CoreOS, would "integrate concepts, technology, and the user experience of Container Linux. This offering is intended to ultimately supersede Atomic Host and function as Red Hat’s immutable, container-centric operating system."
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RedHat Enterprise Linux CoreOS (RHCOS) is now the default operating system for cluster machines in the OpenShift Container Platform. Further, RHCOS is the “only supported operating system for OpenShift Container Platform control plane machines,” and supported only as an OpenShift component. In other words, RHCOS exists solely as part of OpenShift.
Users who want something similar outside the context of OpenShift are directed to Fedora CoreOS, the community version, which is "the official successor to CoreOS Container Linux," according to the end of life announcement. That said, Red Hat has admitted: "Fedora CoreOS cannot currently replace Container Linux for all use cases."
Issues include lack of native support for "Azure, DigitalOcean, GCE, Vagrant, or the Container Linux community-supported platforms" – though it does run on numerous platforms, including AWS, Azure, GCP, Alibaba, VMWare and OpenStack. Further, Fedora CoreOS does not include the rkt container runtime.
Fedora CoreOS officially came out of preview in January but comes with a health warning about no "guarantees about stability."
The team said: "We've found that the incremental, exploratory, forward-looking development required for Fedora CoreOS — which is also a cornerstone of the Fedora Project as a whole — is difficult to reconcile with the iron-clad stability guarantee that ideally exists when automatically updating systems."
Red Hat noted there is a fork of CoreOS Container Linux called Flatcar Linux which may be more suitable for users who do not want to jump into OpenShift. Flatcar Linux is supported by a Berlin company called Kinvolk.
The end of life timeline for CoreOS Container Linux is aggressive, Red Hat said. May 26 is the last date for updates including security patches. From September 1st, "published resources related to CoreOS Container Linux will be deleted or made read-only. OS downloads will be removed, CoreUpdate servers will be shut down, and OS images will be removed from AWS, Azure, and Google Compute Engine. GitHub repositories, including the issue tracker, will become read-only." The reason for deleting OS images is to discourage continued use after end of support.
The problem here is that Fedora CoreOS is not an exact replacement for CoreOS Container Linux and comes with caveats that deter production use, given that in this particular niche, stability is a high priority. ®