Flatcar Container Linux is moving to CGroupsV2

[jepio]

Dear Flatcar Community,

With the Alpha Release v2969.0.0, as described in our recent blog post https://kinvolk.io/blog/2021/09/flatcar-linux-is-moving-to-cgroupsv2/, we are bringing unified cgroups (CGroupsV2) to newly provisioned Flatcar nodes. This is a major change and we intend to make the transition as smooth as possible for existing users. We have made the decision to keep nodes deployed prior to v2969.0.0 on CGroupsV1; they will therefore require manual migration as described further below.

These changes are entering the Alpha channel now and will roll into the Stable channel in the next 2 months. We urge all users to check the impact now by testing the alpha release and reporting issues.

Everything you need to know is summarized at https://kinvolk.io/docs/flatcar-container-linux/latest/container-runtimes/switching-to-unified-cgroups/. Here’s a walkthrough of what the changes mean in a couple of scenarios:

Nodes deployed prior to v2969.0.0

Nodes deployed prior to v2969.0.0 currently use CGroupsV1 and will maintain that configuration when upgrading to 2969+. To manually reconfigure the node to CGroupsV2, follow the instructions at https://kinvolk.io/docs/flatcar-container-linux/latest/container-runtimes/switching-to-unified-cgroups/#migrating-old-nodes-to-unified-cgroups . If you’re running Kubernetes or have a customized Docker/Container configuration keep reading.

Nodes deployed after v2969.0.0

Nodes deployed after v2969.0.0 will start with CGroupsV2. If you are deploying Kubernetes v1.19+, things should continue working. Check whether your deployment hardcodes cgroup drivers anywhere (Ignition/Kubelet/Docker/containerd) – Flatcar users should now use the systemd cgroup driver; our images are configured correctly out-of-the box. Deploying Kubernetes v1.18 or lower will no longer work. Kubernetes v1.18 is not actively maintained, so please find a way to upgrade or use older Flatcar images to seed your deployments.

If you are running custom Docker binaries or custom Docker/containerd configuration

Flatcar now ships with Docker 20.10! Check whether you still need custom binaries. Also check that your configuration works with CGroupsV2 – you should be using the systemd cgroup driver everywhere.

If you run Kubernetes

Be aware of the differences between nodes deployed prior to v2969.0 and those deployed after. We recommend spinning up new nodes with updated configuration using systemd cgroup driver and CGroupsV2 instead of modifying the configuration on running nodes. See https://kinvolk.io/docs/flatcar-container-linux/latest/container-runtimes/switching-to-unified-cgroups/#kubernetes for more information.

Should you encounter issues caused by the switch, feel free to reach out on the issue tracker https://github.com/kinvolk/Flatcar or matrix https://app.element.io/#/room/#flatcar:matrix.org

The Flatcar Team