Booting Flatcar Container Linux via iPXE

    These instructions will walk you through booting Flatcar Container Linux via iPXE on real or virtual hardware. By default, this will run Flatcar Container Linux completely out of RAM. Flatcar Container Linux can also be installed to disk .

    A minimum of 3 GB of RAM is required to boot Flatcar Container Linux via PXE.

    Configuring iPXE

    iPXE can be used on any platform that can boot an ISO image. This includes many cloud providers and physical hardware.

    To illustrate iPXE in action we will use qemu-kvm in this guide.

    Setting up iPXE boot script

    When configuring the Flatcar Container Linux iPXE boot script there are a few kernel options that may be useful but all are optional.

    • rootfstype=tmpfs: Use tmpfs for the writable root filesystem. This is the default behavior.
    • rootfstype=btrfs: Use btrfs in RAM for the writable root filesystem. The filesystem will consume more RAM as it grows, up to a max of 50%. The limit isn’t currently configurable.
    • root: Use a local filesystem for root instead of one of two in-ram options above. The filesystem must be formatted (perhaps using Ignition) but may be completely blank; it will be initialized on boot. The filesystem may be specified by any of the usual ways including device, label, or UUID; e.g: root=/dev/sda1, root=LABEL=ROOT or root=UUID=2c618316-d17a-4688-b43b-aa19d97ea821.
    • sshkey: Add the given SSH public key to the core user’s authorized_keys file. Replace the example key below with your own (it is usually in ~/.ssh/id_rsa.pub)
    • console: Enable kernel output and a login prompt on a given tty. The default, tty0, generally maps to VGA. Can be used multiple times, e.g. console=tty0 console=ttyS0
    • flatcar.autologin: Drop directly to a shell on a given console without prompting for a password. Useful for troubleshooting but use with caution. For any console that doesn’t normally get a login prompt by default be sure to combine with the console option, e.g. console=tty0 console=ttyS0 flatcar.autologin=tty1 flatcar.autologin=ttyS0. Without any argument it enables access on all consoles. Note that for the VGA console the login prompts are on virtual terminals (tty1, tty2, etc), not the VGA console itself (tty0).
    • flatcar.first_boot=1: Download an Ignition config and use it to provision your booted system. Ignition configs are generated from Container Linux Configs. See the config transpiler documentation for more information. If a local filesystem is used for the root partition, pass this parameter only on the first boot.
    • ignition.config.url: Download the Ignition config from the specified URL. http, https, s3, and tftp schemes are supported.
    • ip: Configure temporary static networking for initramfs. This parameter does not influence the final network configuration of the node and is mostly useful for first-boot provisioning of systems in DHCP-less environments. See Ignition documentation for the complete syntax.

    Choose a Channel

    Flatcar Container Linux is designed to be updated automatically with different schedules per channel. You can disable this feature , although we don’t recommend it. Read the release notes for specific features and bug fixes.

    Setting up the Boot Script

    The Alpha channel closely tracks master and is released frequently. The newest versions of system libraries and utilities will be available for testing. The current version is Flatcar Container Linux 4116.0.0.

    iPXE downloads a boot script from a publicly available URL. You will need to host this URL somewhere public and replace the example SSH key with your own. You can also run a custom iPXE server.

    #!ipxe
    

    set base-url http://alpha.release.flatcar-linux.net/amd64-usr/current kernel ${base-url}/flatcar_production_pxe.vmlinuz initrd=flatcar_production_pxe_image.cpio.gz flatcar.first_boot=1 ignition.config.url=https://example.com/pxe-config.ign initrd ${base-url}/flatcar_production_pxe_image.cpio.gz boot

    The Beta channel consists of promoted Alpha releases. The current version is Flatcar Container Linux 4081.1.0.

    iPXE downloads a boot script from a publicly available URL. You will need to host this URL somewhere public and replace the example SSH key with your own. You can also run a custom iPXE server.

    #!ipxe

    set base-url http://beta.release.flatcar-linux.net/amd64-usr/current kernel ${base-url}/flatcar_production_pxe.vmlinuz initrd=flatcar_production_pxe_image.cpio.gz flatcar.first_boot=1 ignition.config.url=https://example.com/pxe-config.ign initrd ${base-url}/flatcar_production_pxe_image.cpio.gz boot

    The Stable channel should be used by production clusters. Versions of Flatcar Container Linux are battle-tested within the Beta and Alpha channels before being promoted. The current version is Flatcar Container Linux 3975.2.2.

    iPXE downloads a boot script from a publicly available URL. You will need to host this URL somewhere public and replace the example SSH key with your own. You can also run a custom iPXE server.

    #!ipxe

    set base-url http://stable.release.flatcar-linux.net/amd64-usr/current kernel ${base-url}/flatcar_production_pxe.vmlinuz initrd=flatcar_production_pxe_image.cpio.gz flatcar.first_boot=1 ignition.config.url=https://example.com/pxe-config.ign initrd ${base-url}/flatcar_production_pxe_image.cpio.gz boot

    An easy place to host this boot script is on http://pastie.org . Be sure to reference the “raw” version of script, which is accessed by clicking on the clipboard in the top right.

    Butane Configs

    Flatcar Container Linux allows you to configure machine parameters, configure networking, launch systemd units on startup, and more via Butane Configs. These configs are then transpiled into Ignition configs and given to booting machines. Head over to the docs to learn about the supported features .

    You can provide a raw Ignition JSON config to Flatcar Container Linux via the ignition.config.url specified above.

    As an example, this Butane YAML config will start an NGINX Docker container:

    variant: flatcar
    version: 1.0.0
    systemd:
      units:
        - name: nginx.service
          enabled: true
          contents: |
            [Unit]
            Description=NGINX example
            After=docker.service
            Requires=docker.service
            [Service]
            TimeoutStartSec=0
            ExecStartPre=-/usr/bin/docker rm --force nginx1
            ExecStart=/usr/bin/docker run --name nginx1 --pull always --log-driver=journald --net host docker.io/nginx:1
            ExecStop=/usr/bin/docker stop nginx1
            Restart=always
            RestartSec=5s
            [Install]
            WantedBy=multi-user.target        
    

    Transpile it to Ignition JSON:

    cat cl.yaml | docker run --rm -i quay.io/coreos/butane:latest > ignition.json
    

    Booting iPXE

    First, download and boot the iPXE image. We will use qemu-kvm in this guide but use whatever process you normally use for booting an ISO on your platform.

    wget http://boot.ipxe.org/ipxe.iso
    qemu-kvm -m 1024 ipxe.iso -display curses
    

    Next press Ctrl+B to get to the iPXE prompt and type in the following commands:

    iPXE> dhcp
    iPXE> chain http://${YOUR_BOOT_URL}
    

    Immediately iPXE should download your boot script URL and start grabbing the images from the Flatcar Container Linux storage site:

    ${YOUR_BOOT_URL}... ok
    http://alpha.release.flatcar-linux.net/amd64-usr/current/flatcar_production_pxe.vmlinuz... 98%
    

    After a few moments of downloading Flatcar Container Linux should boot normally.

    Update process

    Since Flatcar Container Linux’s upgrade process requires a disk, this image does not have the option to update itself. Instead, the box simply needs to be rebooted and will be running the latest version, assuming that the image served by the PXE server is regularly updated.

    Installation

    Flatcar Container Linux can be completely installed on disk or run from RAM but store user data on disk. Read more in our Installing Flatcar Container Linux guide .

    Adding a custom OEM

    Similar to the OEM partition in Flatcar Container Linux disk images, iPXE images can be customized with an Ignition config bundled in the initramfs. You can view the instructions on the PXE docs .

    Using Flatcar Container Linux

    Now that you have a machine booted it is time to play around. Check out the Flatcar Container Linux Quickstart guide or dig into more specific topics .