Migrating from CoreOS Container Linux

While Flatcar is compatible with CoreOS Container Linux there are some naming differences you need to be aware of.

NOTE: See Updating from Container Linux for additional information on updating an existing cluster.


Instead of coreos-installer you need to use flatcar-installer.

Kernel command line parameters

Instead of providing the coreos.first_boot=1 argument via the boot loader you need to provide flatcar.first_boot=1. This forces provisioning via Ignition even if the machine (image) was booted already before.

Instead of providing the coreos.config.url=SOMEURL argument via the boot loader you need to provide ignition.config.url=SOMEURL to tell Ignition to download the configuration. The change to a more generic name was done upstream by the Ignition project. Version 0.33 still supports both names and we also do this via the analogous flatcar.config.url option but we encourage the generic name because future versions of Ignition will only support ignition.config.url.

Ignition configuration with QEMU

Instead of using opt/com.coreos/config in the -fw_cfg name-value argument pair for QEMU/KVM or libvirt you need to use opt/org.flatcar-linux/config. The value in the argument pair specifies the Ignition file to use.

Ignition configuration with VMware

Instead of coreos.config.data and coreos.config.data.encoding for the VMware guestinfo.VARIABLE command line options you need to use ignition.config.data and ignition.config.data.encoding. As for the kernel parameter this change was done upstream by the Ignition project.