Flatcar Linux - Rafay Product Documentation

Upstream Kubernetes on Flatcar Linux using Rafay

This blog is Part 3 of our series on Flatcar Linux and Kubernetes

Our upcoming February release will introduce a number of new features and enhancements. We will write about these in separate blogs. This blog is focused on support for Upstream Kubernetes based on Rafay MKS on nodes running Flatcar Linux. The Rafay platform enables users to seamlessly provision new clusters and perform in-place upgrades of Kubernetes clusters, simplifying lifecycle management.

For more details on Flatcar Linux, visit the official Flatcar Linux website.

Provision Cluster

Rafay MKS based Upstream Kubernetes clusters can be configured and provisioned on Flatcar Linux using all the supported interfaces:

In this blog, we will demonstrate this using the web console and the Rafay RCTL CLI.

Install Flatcar-Part 2

This is in continuation of our first blog where we introduced Flatcar Linux. In part 2, we will show how you can install a Flatcar Container Linux instance locally on your laptop so that you can learn more about it. This guide will take you through the steps to install it, boot the instance, SSH into it. Finally, we will explore and validate some of Flatcar's critical features that we reviewed in the first blog.

Boot Flatcar Instance Locally

Follow the steps below to download, set up, and run a Flatcar instance locally. In our example, we are installing this on a M1 MacBook Pro.

Step 1: Install QEMU

First, install QEMU on your system. Follow the instructions provided here.

Step 2: Download the QEMU Script and Flatcar Image

Get the QEMU helper script and the latest stable Flatcar image

wget https://stable.release.flatcar-linux.net/amd64-usr/current/flatcar_production_qemu.sh
wget https://stable.release.flatcar-linux.net/amd64-usr/current/flatcar_production_qemu_image.img.bz2

Step 3: Extract the Image

Decompress the downloaded image

bzip2 --decompress --keep flatcar_production_qemu_image.img.bz2

Step 4: Make the Script Executable

Set execution permissions for the QEMU helper script:

chmod +x flatcar_production_qemu.sh

Step 5: Create/Start the Flatcar Instance

Use the following command to start the Flatcar instance with 4 CPUs and 4GB memory in console mode:

./flatcar_production_qemu.sh -M 4096 -- -smp 4 -display curses

Access Flatcar Instance via SSH

Once the Flatcar instance is running, set up your SSH configuration to connect to it. Update your SSH config file as follows:

# ~/.ssh/config
Host flatcar
        User core
        StrictHostKeyChecking no
        UserKnownHostsFile /dev/null
        HostName 127.0.0.1
        Port 2222

You can then SSH into the instance using the following command:

ssh flatcar

After you successfully SSH into the instance, you can run the following command to verify the system's firmware and kernel details:

hostnamectl

You should see something like the image below.

Flatcar Versioning

In the image above, notice that the Flatcar version is 4081.2.1. Here’s how the versioning system works for Flatcar Linux.

In our version (4081.2.1), 2 represents a stable release on its first patch.

Explore Flatcar's Key Features

Now that we have installed Flatcar Linux, let us test and validate some of the interesting features of Flatcar.

1. No Package Manager and Immutable File System

In Linux, the /usr directory is used to store user system resources. It contains the majority of the system’s software and programs i.e. binaries, libraries, documentation, and other files shared by all users of the system. Flatcar Linux makes the /usr directory read-only as part of its design philosophy to ensure system immutability and reliability. By focusing on immutability and containerization, Flatcar Linux achieves a stable, predictable, and secure platform, which is why /usr is deliberately set to read-only.

Let's test whether Flatcar Linux's /usr folder is immutable

You will notice they are unavailable. Additionally, any attempt to write to the /usr/ directory will show that the file system is immutable. For example, let's try to create a new file in the /usr directory using the "touch" command.

sudo touch /usr/test

Below is an example screenshot showing this behavior:

2. Automatic Updates

Flatcar includes an auto-update system by default. By default, the Flatcar instance will check for updates every hour, download them if available, and automatically reboot to apply updates to ensure that your instance is always current and up to date. Organizations can always self-host their own update server ensuring that they can control how/when their Flatcar instances are kept current.

To view the update configuration, run the following command inside the Flatcar instance:

cat /usr/share/flatcar/update.conf

The output will look like this:

SERVER=https://public.update.flatcar-linux.net/v1/update/
GROUP=stable

Administrators can customize the default behavior by configuring the upgrade strategy. For example, a common configuration is for administrators to specify "maintenance windows" for reboots.

Other Installation Methods

If you’re not using QEMU, you can install Flatcar Container Linux on other platforms like VirtualBox, Vagrant, and others. You can find detailed installation instructions for these platforms here. Flatcar also provides prebuilt images for cloud providers like AWS, Azure, Google Cloud, and others. These cloud platforms offer Flatcar-based AMIs or images to streamline deployment. Check out the cloud-specific installation steps here.

Conclusion

In this blog, we:

In the upcoming Part 3 of the blog series on Flatcar Linux, we will cover how to install Rafay's Kubernetes Distribution (Rafay MKS) on Flatcar and manage it centrally using the Rafay Platform.