Blog on Flatcar Container Linux

Learning from the Flatcar DNS Outage – A Post-Mortem

Thu, 27 Feb 2025 00:22:13 +0200

On February 2nd and 3rd, 2025, Flatcar experienced a significant DNS outage that affected our update and release servers, as well as parts of our CI/CD infrastructure. As a result, users were unable to download new Flatcar releases, retrieve Flatcar images for several hours. The root cause was a miscommunication during a domain transfer, which led to DNS mis-configurations.

In collaboration with the Linux Foundation (LF) IT team, we have conducted a full post-mortem analysis to understand the issue, improve our processes, and ensure greater reliability for the Flatcar community moving forward.

Flatcar train destination: FOSDEM 2025

Fri, 14 Feb 2025 00:22:13 +0200

Attending FOSDEM 2025 was an exhilarating experience for the maintainer team. From the moment we arrived, the energy and enthusiasm of the open-source community were palpable. This year’s event was particularly special for us as it marked our first time having a Flatcar booth, shared with our friends from Gentoo. The diversity of devrooms and the opportunity to engage with contributors and users from around the world made it an unforgettable experience.

What's new in Stable 3975.2.0

Wed, 07 Aug 2024 00:00:00 +0000

What’s new?

Stable 3975.2.0 introduces a wide range of features, packages updates, and security fixes. The major release focusses on introducing support for new vendors, new officially maintained sysexts.

New vendors

Over the past few months, the team has continued to invest in Flatcar support on cloud providers, enhancing existing support with better documentation and an improved user experience. Flatcar Stable now supports Hetzner and Scaleway, as well as KubeVirt images.

OS innovation with systemd-sysext

Wed, 24 Apr 2024 10:22:13 +0200

Flatcar Container Linux has a strong focus on backwards compatibility. Being a continuation of the CoreOS Container Linux project which started more than 10 years ago, the main design stayed as is. Flatcar ships a fixed set of software and users should rely on containers for the rest. This has proven successful but there are some scenarios where one has to extend Flatcar in ways the original design wasn’t intended for. Luckily, Flatcar still evolves, though, to make it even more suited for reliable infrastructure automation.

Extending Flatcar: Say 'Goodbye' to torcx and 'Hello' to systemd-sysext

Mon, 18 Dec 2023 10:22:13 +0200

Flatcar is a minimal, immutable, image-based operating system for fully automated, zero-touch container infrastructure. It ships the bare minimum required for running containers at scale - and usually, the answer to questions like “how do I install tool XYZ on Flatcar?” is: “run it in a container”. Sometimes though, “tool XYZ” needs to operate close to the OS itself, and it’s not feasible (or even outright impossible) to run it in a container. Good examples for such tools and applications are custom container runtimes like podman, complex control planes like Kubernetes, and vendor-specific programs like VMware’s open-vm-tools that are only useful in specific environments.

Summer 2023 - My internship experience

Tue, 25 Jul 2023 14:00:00 +0200

In this blog post, I’ll talk about my enriching internship experience with the Flatcar team. I’ll give you some insight into what I worked on, what I learnt and some of the highlights of my experience.

My work

I interned with the Flatcar team for 2 months from June 5th till July 25th 2023.

The SparkNotes version: we’re a community driven, fully open source, minimal, secure by default and always up-to-date container host Linux distribution. It doesn’t feature a package manager (no apt!), and all OS components reside in a protected read-only partition. The build system for the OS takes after CoreOS’ build system which itself is derived from ChromeOS.

About the handling of embargoed security issues

Mon, 07 Nov 2022 14:00:00 +0200

TL; DR: Flatcar is safe against recent OpenSSL vulnerabilities

With the recent OpenSSL vulnerabilities CVE-2022-3786 and CVE-2022-3602 , the Flatcar team has provided as soon as possible a batch of releases for impacted Flatcar channels (all except LTS which is not impacted). Releases have been published within one hour after the official public announcement and users were able to secure their workloads almost immediately without unexpected turbulences as the releases included only minimal changes to address the security issues.

Measuring energy consumption

Sun, 09 Oct 2022 20:00:00 +0200

In the last decade, with the increase of components inside Ops infrastructures, monitoring has started to be more than ever a central component. Having a monitored infrastructure helps to not navigate blindly inside a constellation of services and to be pro-active on issues. Monitoring can be defined as a shaped form of metrics and these metrics are often divided into two categories: applicative and system. In this blogpost, let’s put on our Scaphandre to dive into an unusual system metric: the energy.

FrOSCon 2022 - Summary of an Open-Source week-end with some Flatcar team members

Tue, 13 Sep 2022 14:00:00 +0200

FrOSCon took place this year from 20 to 21 August 2022, a two-day event about Free Software and Open Source in Sankt-Augustin, Germany. FrOSCon has something very unique as a conference: it’s almost a large family. One reason is that for many attendees it has become a tradition to go there, building friendships, over 10 years or more. On top of that, it was the first FrOSCon after two years of the event being cancelled or remote-only.

Flatcar Container Linux Long-Term Support (LTS) channel and advanced features now available to community

Tue, 10 May 2022 14:00:00 +0200

We are pleased to announce some significant enhancements to Flatcar Container Linux community images, with a Long-Term Support (LTS) channel and some advanced features that were previously only available to Kinvolk subscription customers. These changes are in response to requests from users and follow through on our commitment that the project be led by the community.

LTS

Flatcar Container Linux LTS is a family of release channels dedicated to users who want a slower-moving update cadence, for example because they are running workloads with an elevated infrastructure maintenance cost. Each Flatcar LTS release is based on an LTS upstream kernel and kept up to date with critical patch fixes including for security vulnerabilities but will not receive new Flatcar features or major package or component version updates, ensuring maximum stability for applications while simplifying operations and maintaining security compliance.

OpenSSL-3.0.0 on Flatcar: what to expect?

Wed, 27 Oct 2021 20:00:00 +0200

In the Open-Source Software ecosystem, actions often start with an opened issue. In this journey, it was the flatcar-linux/Flatcar#418 - but before talking about OpenSSL-3.0 on Flatcar, let’s take two steps back.

TL; DR: Let’s upgrade to OpenSSL v3 for a whole operating system and spoiler alert, the issue was misleading: almost nothing broke.

Flatcar Container Linux (FCL) is an open-source Linux distro, optimized to run container workloads and based on Gentoo. One particularity of FCL is the lack of package manager: it’s not possible to install softwares with tools like emerge, pacman or yum - this design ensures reproducibility and security. It’s the responsibility of the community and the FCL core maintainers to manage the lifecycle of packages: from selection to the upgrades and applying FCL patches.

7 Fun Flatcar Facts from our Community Survey

Wed, 08 Sep 2021 10:00:00 +0200

We recently asked the Flatcar user community to share their experiences deploying Flatcar Container Linux. We promised to share the results back with the community, and so here are the top 7 take-aways from the survey:

#1 Kubernetes is deployed on more than 4 out of 5 Flatcar deployments

No surprise here, since Flatcar is designed for containers and Kubernetes is the most popular container orchestration system, 82% of Flatcar users reported that they ran Kubernetes.

Flatcar Container Linux is moving to CGroupsV2

Wed, 01 Sep 2021 20:00:00 +0200

Flatcar Container Linux v2969.0.0 was released to the Alpha channel on Aug 19, 2021. This release brings a big change to the underlying configuration of the OS: the default control groups hierarchy has been switched to CGroupsV2. This blog post explains why these changes are necessary and how they will impact users.

cgroup

Linux namespaces and control groups (or cgroups) are the core building blocks of containers on Linux. Cgroups restrict the resources (CPU, memory, I/O) that a process or container can consume, which is essential to securely hosting diverse workloads on the same system.

Using eBPF in Flatcar Container Linux

Thu, 22 Apr 2021 10:00:00 +0200

Extended Berkeley Packet Filter (eBPF) is a core Linux technology with multiple applications in different computer domains like security, networking and tracing. For the containers and Kubernetes specific case, it’s used with networking projects like Cilium or Calico, debugging solutions like BCC, kubectl-trace and Inspektor Gadget, and security-related projects like tracee and Falco.

eBPF is a very fast evolving technology: each new kernel release includes new features, and different Linux distributions rush to enable them for their users. Flatcar Container Linux is no exception, and in this blog post I cover the new eBPF features that we have enabled in the lastest Flatcar versions and why they are important.

Container Linux: Back on Track with Flatcar

Wed, 27 May 2020 08:00:00 -0700

Yesterday, CoreOS Container Linux reached its end of life (EOL). Today marks the beginning of Flatcar Container Linux as an independent Linux distribution. With this comes a certain responsibility, but more notably: an opportunity for Kinvolk and the broader container community.

Just after the EOL announcement this February, Chris wrote a post about what this would mean for Kinvolk and the Flatcar project . Now that the end-of-life has come to pass, I’d like to build on Chris’ post, go further into where we go from here, and the reasons I’m excited to be at Kinvolk.

Running Flatcar Container Linux in Microsoft Azure

Fri, 24 Apr 2020 17:13:00 +0200

Recently, we showed how easy it is to migrate from CoreOS Container Linux to Flatcar Container Linux . Today we’re going to build on that to show how to start instances of Flatcar Container Linux on Azure and how to migrate existing Azure instances running CoreOS Container Linux.

Note: Red Hat announced CoreOS Container Linux will reach its end-of-life on May 26 . Flatcar Container Linux is the only drop-in replacement going forward.

VMware and Kinvolk bring Flatcar Container Linux to vSphere, providing supported path forward for CoreOS users

Tue, 21 Apr 2020 12:30:00 +0200

Recently, we have been working with many end users who, faced with the imminent end-of-life of CoreOS Container Linux, are migrating to Flatcar Container Linux as the secure foundation for their container deployments. And, with the majority of enterprises adopting vSphere for their private clouds¹, we have heard from many of those users that fully certified support for vSphere is an important consideration in their migration decision.

Today, we are pleased to share details of our collaboration with VMware to enable the deployment of Flatcar Container Linux in a fully-supported vSphere environment. There are a number of important elements to this:

Steps to Migrate from CoreOS to Flatcar Container Linux

Wed, 18 Mar 2020 17:00:00 +0100

Flatcar Container Linux is a drop-in replacement for CoreOS Container Linux. Thus, one should think that a migration should be an effortless task, and it is.

Since Red Hat announced that CoreOS Container Linux will reach its end-of-life on May 26 , we’ve seen a major uptick in the usage of Flatcar Container Linux. We’ve also had a number of questions about the migration process. This post looks to highlight how to migrate to Flatcar Container Linux in two ways; modifying your deployment to install Flatcar Container Linux, and updating directly from CoreOS Container Linux.

Flatcar Container Linux enters new era after CoreOS End-of-Life announcement

Mon, 24 Feb 2020 12:10:00 -0700

Almost two years ago, we launched Flatcar Container Linux , a drop-in replacement for CoreOS Container Linux. Since then, we’ve made almost 200 releases , added an experimental edge channel , released the update server - Nebraska , (re-)introduced ARM support (which had been dropped by Red Hat), and introduced the Kinvolk Flatcar Container Linux Subscription .

But Flatcar Container Linux is about to enter a new era.

The New Era

Earlier this month, Red Hat announced the End of Life of CoreOS Container Linux will be May 26th. This was something that had been expected since soon after the CoreOS acquisition was announced; everyone knew it was coming, but now we have dates.

Announcing the Kinvolk Update Service and Nebraska Project

Thu, 07 Nov 2019 16:25:00 +0100

In this post, we’ll dive into the details of Kinvolk Update Service and share more about the heritage, functionality, and implementation. Of course, Kinvolk Update Service is built on 100% Open Source Software, which we are also making available today on github as the Nebraska project.

Motivation

When having a number of Flatcar Container Linux instances that compose a cluster, it is useful to have a tool to roll out updates, and to monitor the status of the instances and the updates progress. i.e. How many instances are currently downloading version X.Y.Z in our cluster? And how many should be updated to the new beta version?

Flatcar Linux is now open to the public

Mon, 30 Apr 2018 12:00:00 +0200

A few weeks ago we announced Flatcar Linux , our effort to create a commercially supported fork of CoreOS’ container Linux . You can find the reasoning for the fork in our FAQ .

Since then we’ve been testing, improving our build process, establishing security procedures, and talking to testers about their experiences. We are now satisfied that Flatcar Linux is a stable and reliable container operating system that can be used in production clusters.

Announcing the Flatcar Linux project

Tue, 06 Mar 2018 17:05:56 +0200

Today Kinvolk announces Flatcar Linux , an immutable Linux distribution for containers. With this announcement, Kinvolk is opening the Flatcar Linux project to early testers. If you are interested in becoming a tester and willing to provide feedback, please let us know .

Flatcar Linux is a friendly fork of CoreOS’ Container Linux and as such, compatible with it. It is independently built, distributed and supported by the Kinvolk team.

Why fork Container Linux?

At Kinvolk, we provide support and engineering services for foundational open-source Linux projects used in cloud infrastructure. Last year we started getting inquiries about providing support for Container Linux. Since those inquiries, we had been thinking about how we could offer such support.