OKD Foundations Video Series: FCOS and SCOS

Summary

The video discusses Fedora CoreOS (Fedora Chorus), its features, and how it fits into OKD. Fedora CoreOS is an official Fedora edition designed for both single-node and cluster environments, focusing on automatic updates, provisioning, and immutable infrastructure. The speaker explains RPM-OSTree, the hybrid package system enabling atomic updates and rollbacks. It also introduces Ignition for automating node provisioning and configuration. The video covers Fedora CoreOS' distribution through streams (next, testing, stable) and its differences from CentOS Stream CoreOS, as well as their roles in OKD, with key distinctions in update mechanisms and additional tooling.

Takeaways

• 📦 Fedora CoreOS (FCoS) is an official Fedora edition focused on single-node and cluster use cases, particularly useful for OKD environments.
• 🖥️ FCoS integrates ideas from CoreOS Container Linux and Fedora Atomic Host, blending cloud-native provisioning with robust update mechanisms.
• 🔄 The core philosophy of FCoS is built around automatic updates and provisioning by default, enabling easier management of clusters with immutable infrastructure.
• ⚙️ Ignition is used for configuring nodes in FCoS on first boot, allowing automation of setup and making it simpler to re-provision nodes with consistent configurations.
• 🖥️ RPM-OSTree is used in FCoS for image-based system updates, similar to version control like Git, allowing for atomic updates and easy rollbacks.
• 🚀 FCoS supports multiple installation methods, including live ISO, PXE boot, and raw disk images, compatible with both cloud and bare-metal environments.
• 🧪 Fedora CoreOS has three streams—Next, Testing, and Stable—ensuring that updates are tested thoroughly before reaching general availability.
• ☁️ OKD uses a modified version of Fedora CoreOS with automatic updates disabled, as cluster-level updates manage the node updates within OKD.
• 🌍 FCoS supports a variety of cloud platforms like AWS and GCP, as well as architectures such as x86_64, aarch64, and more.
• 🔄 CentOS Stream CoreOS is a counterpart to Fedora CoreOS, based on CentOS Stream packages, offering a slower pace of change suitable for Red Hat Enterprise Linux (RHEL) alignment.

Q & A

What is Fedora CoreOS and when was it officially introduced?

Fedora CoreOS is an official Fedora edition focused on both single-node and cluster use cases. It was officially introduced in Fedora 37.

What are the three main pillars of Fedora CoreOS?

The three main pillars of Fedora CoreOS are automatic updates by default, automatic provisioning, and support for immutable infrastructure.

What two container-first operating systems is Fedora CoreOS a successor to?

Fedora CoreOS is the successor to CoreOS Container Linux and Fedora Atomic Host.

What platforms and architectures are supported by Fedora CoreOS?

Fedora CoreOS supports various cloud and virtualization platforms such as AWS and GCP, as well as bare-metal infrastructure through live ISOs, PXE booting, and raw disk images. It supports four architectures: x86_64, aarch64, s390x, and ppc64le.

How does RPM-OSTree work in Fedora CoreOS?

RPM-OSTree is a hybrid package/image system that allows automatic upgrades. It works similarly to Git by storing all system files in a repository, enabling atomic updates and rollback capabilities.

What is Ignition and what role does it play in Fedora CoreOS?

Ignition is a tool used in Fedora CoreOS for automating the provisioning and configuration of nodes during their first boot. It allows administrators to automate system setup using a declarative JSON configuration.

What are the three streams in which Fedora CoreOS is available?

Fedora CoreOS is available in three streams: next, testing, and stable. The next stream is for future versions, the testing stream is for release candidates, and the stable stream receives updates two weeks after testing.

How are updates handled in Fedora CoreOS?

Updates in Fedora CoreOS are managed through streams (next, testing, stable) and are tested extensively on cloud platforms and QEMU to ensure stability. Updates are atomic and can be rolled back if necessary.

What is the difference between Fedora CoreOS and CentOS Stream CoreOS?

Fedora CoreOS is based on Fedora packages and receives updates frequently (every six months), while CentOS Stream CoreOS is based on CentOS Stream packages, which are upstream of Red Hat Enterprise Linux and have a slower release cycle.

How does OKD use Fedora CoreOS and CentOS Stream CoreOS?

OKD has two flavors: one based on Fedora CoreOS and another on CentOS Stream CoreOS (called OKD ESoS). In OKD, automatic updates are disabled, and node updates are managed by the cluster. It also includes additional tools like CRI-O and OC.