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External runtime dependencies#

k0s is packaged as a single binary, which includes all the needed components. All the binaries are statically linked which means that in typical use cases there's an absolute minimum of external runtime dependencies.

However, depending on the node role and cluster configuration, some of the underlying components may have specific dependencies, like OS level tools, packages and libraries. This page aims to provide a comprehensive overview.

The following command checks for known requirements on a host (currently only available on Linux):

k0s sysinfo

A unique machine ID for multi-node setups#

Whenever k0s is run in a multi-node setup (i.e. the --single command line flag isn't used), k0s requires a machine ID: a unique host identifier that is somewhat stable across reboots. For Linux, this ID is read from the files /var/lib/dbus/machine-id or /etc/machine-id. For Windows, it's taken from the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\MachineGuid. If neither of the OS specific sources yield a result, k0s will fallback to use a machine ID based on the hostname.

When running k0s on top of virtualized or containerized environments, you need to ensure that hosts get their own unique IDs, even if they have been created from the same image.

Linux specific#

Linux kernel configuration#

Needless to say, as k0s operates Kubernetes worker nodes, there's a certain number of needed Linux kernel modules and configurations that we need in the system. This basically stems from the need to run both containers and also be able to set up networking for the containers.

The needed kernel configuration items are listed below. All of them are available in Kernel versions 4.3 and above. If running on older kernels, check if the distro in use has backported some features; nevertheless, it might meet the requirements. k0s will check the Linux kernel release as part of its pre-flight checks and issue a warning if it's below 3.10.

The list covers ONLY the k0s/kubernetes components’ needs on worker nodes. Your own workloads may require more.

Note: As part of its pre-flight checks, k0s will try to inspect and validate the kernel configuration. In order for that to succeed, the configuration needs to be accessible at runtime. There are some typical places that k0s will check. A bullet-proof way to ensure the accessibility is to enable CONFIG_IKCONFIG_PROC, and, if enabled as a module, to load the configs module: modprobe configs.

Control Groups (cgroups)#

Both cgroup v1 and cgroup v2 are supported.

Required cgroup controllers:

  • cpu
  • cpuacct
  • cpuset
  • memory
  • devices
  • freezer
  • pids

Optional cgroup controllers:

containerd and AppArmor#

In order to use containerd in conjunction with AppArmor, it must be enabled in the kernel and the /sbin/apparmor_parser executable must be installed on the host, otherwise containerd will disable AppArmor support.

Other dependencies in previous versions of k0s#

  • up until k0s v1.21.9+k0s.0: iptables
    Required for worker nodes. Resolved by @ncopa in #1046 by adding iptables and friends to k0s's embedded binaries.

Windows specific#