k0sctl

A command-line bootstrapping and management tool for k0s zero friction kubernetes clusters.

• Installation
• Development status
• Usage
• Configuration

Example output of k0sctl deploying a k0s cluster:

INFO ==> Running phase: Connect to hosts
INFO ==> Running phase: Detect host operating systems
INFO [ssh] 10.0.0.1:22: is running Ubuntu 20.10
INFO [ssh] 10.0.0.2:22: is running Ubuntu 20.10
INFO ==> Running phase: Prepare hosts
INFO ==> Running phase: Gather host facts
INFO [ssh] 10.0.0.1:22: discovered 10.12.18.133 as private address
INFO ==> Running phase: Validate hosts
INFO ==> Running phase: Gather k0s facts
INFO ==> Running phase: Download k0s binaries on hosts
INFO ==> Running phase: Configure k0s
INFO ==> Running phase: Initialize the k0s cluster
INFO [ssh] 10.0.0.1:22: installing k0s controller
INFO ==> Running phase: Install workers
INFO [ssh] 10.0.0.1:22: generating token
INFO [ssh] 10.0.0.2:22: installing k0s worker
INFO [ssh] 10.0.0.2:22: waiting for node to become ready
INFO ==> Running phase: Disconnect from hosts
INFO ==> Finished in 2m2s
INFO k0s cluster version 1.22.3+k0s.0 is now installed
INFO Tip: To access the cluster you can now fetch the admin kubeconfig using:
INFO      k0sctl kubeconfig

You can find example Terraform and bootloose configurations in the examples/ directory.

Installation

Install from the released binaries

Download the desired version for your operating system and processor architecture from the k0sctl releases page. Make the file executable and place it in a directory available in your $PATH.

As the released binaries aren't signed yet, on macOS and Windows, you must first run the executable via "Open" in the context menu and allow running it.

Install from the sources

If you have a working Go toolchain, you can use go install to install k0sctl to your $GOPATH/bin.

go install github.com/k0sproject/k0sctl@latest

Package managers

Homebrew (macOS, Linux)

brew install k0sproject/tap/k0sctl

Chocolatey (Windows)

Note: The chocolatey package is community maintained, any issues should be reported to the maintainer of the package.

choco install k0sctl

Shell auto-completions

Bash

k0sctl completion > /etc/bash_completion.d/k0sctl

Zsh

k0sctl completion > /usr/local/share/zsh/site-functions/_k0sctl

Fish

k0sctl completion > ~/.config/fish/completions/k0sctl.fish

Anonymous telemetry

K0sctl sends anonymized telemetry data when it is used. This can be disabled via the --disable-telemetry flag or by setting the environment variable DISABLE_TELEMETRY=true.

The telemetry data includes:

• K0sctl version
• Operating system + CPU architecture ("linux x86", "darwin arm64", ...)
• An anonymous machine ID generated by denisbrodbeck/machineid or if that fails, an md5 sum of the hostname
• Event information:
  • Phase name ("Connecting to hosts", "Gathering facts", ...) and the duration how long it took to finish
  • Cluster UUID (kubectl get -n kube-system namespace kube-system -o template={{.metadata.uid}})
  • Was k0s dynamic config enabled (true/false)
  • Was a custom or the default k0s configuration used (true/false)
  • In case of a crash, a backtrace with source filenames and line numbers only

The data is used to estimate the number of users and to identify failure hotspots.

Development status

K0sctl is ready for use and in continuous development. It is still at a stage where maintaining backwards compatibility is not a high priority goal.

Missing major features include at least:

• The released binaries have not been signed
• The configuration specification and command-line interface options are still evolving

Usage

k0sctl apply

The main function of k0sctl is the k0sctl apply subcommand. Provided a configuration file describing the desired cluster state, k0sctl will connect to the listed hosts, determines the current state of the hosts and configures them as needed to form a k0s cluster.

The default location for the configuration file is k0sctl.yaml in the current working directory. To load a configuration from a different location, use:

k0sctl apply --config path/to/k0sctl.yaml

If the configuration cluster version spec.k0s.version is greater than the version detected on the cluster, a cluster upgrade will be performed. If the configuration lists hosts that are not part of the cluster, they will be configured to run k0s and will be joined to the cluster.

k0sctl init

Generate a configuration template. Use --k0s to include an example spec.k0s.config k0s configuration block. You can also supply a list of host addresses via arguments or stdin.

Output a minimal configuration template:

k0sctl init > k0sctl.yaml

Output an example configuration with a default k0s config:

k0sctl init --k0s > k0sctl.yaml

Create a configuration from a list of host addresses and pipe it to k0sctl apply:

k0sctl init 10.0.0.1 10.0.0.2 [email protected]:8022 | k0sctl apply --config -

k0sctl backup & restore

Takes a backup of the cluster control plane state into the current working directory.

The files are currently named with a running (unix epoch) timestamp, e.g. k0s_backup_1623220591.tar.gz.

Restoring a backup can be done as part of the k0sctl apply command using --restore-from k0s_backup_1623220591.tar.gz flag.

Restoring the cluster state is a full restoration of the cluster control plane state, including:

• Etcd datastore content
• Certificates
• Keys

In general restore is intended to be used as a disaster recovery mechanism and thus it expects that no k0s components actually exist on the controllers.

Known limitations in the current restore process:

• The control plane address (externalAddress) needs to remain the same between backup and restore. This is caused by the fact that all worker node components connect to this address and cannot currently be re-configured.

k0sctl reset

Uninstall k0s from the hosts listed in the configuration.

k0sctl kubeconfig

Connects to the cluster and outputs a kubeconfig file that can be used with kubectl or kubeadm to manage the kubernetes cluster.

Example:

$ k0sctl kubeconfig --config path/to/k0sctl.yaml > k0s.config
$ kubectl get node --kubeconfig k0s.config
NAME      STATUS     ROLES    AGE   VERSION
worker0   NotReady   <none>   10s   v1.20.2-k0s1

Configuration file

The configuration file is in YAML format and loosely resembles the syntax used in Kubernetes. YAML anchors and aliases can be used.

To generate a simple skeleton configuration file, you can use the k0sctl init subcommand.

Configuration example:

apiVersion: k0sctl.k0sproject.io/v1beta1
kind: Cluster
metadata:
  name: my-k0s-cluster
spec:
  hosts:
  - role: controller
    installFlags:
    - --debug
    ssh:
      address: 10.0.0.1
      user: root
      port: 22
      keyPath: ~/.ssh/id_rsa
  - role: worker
    installFlags:
    - --debug
    ssh:
      address: 10.0.0.2
  k0s:
    version: 0.10.0
    config:
      apiVersion: k0s.k0sproject.io/v1beta1
      kind: ClusterConfig
      metadata:
        name: my-k0s-cluster
      spec:
        images:
          calico:
            cni:
              image: calico/cni
              version: v3.16.2

Environment variable substitution

Simple bash-like expressions are supported in the configuration for environment variable substition.

• $VAR or ${VAR} value of VAR environment variable
• ${var:-DEFAULT_VALUE} will use VAR if non-empty, otherwise DEFAULT_VALUE
• $$var - escape, result will be $var.
• And several other expressions

Configuration Header Fields

apiVersion <string> (required)

The configuration file syntax version. Currently the only supported version is k0sctl.k0sproject.io/v1beta1.

kind <string> (required)

In the future, some of the configuration APIs can support multiple types of objects. For now, the only supported kind is Cluster.

spec <mapping> (required)

The main object definition, see below

metadata <mapping> (optional)

Information that can be used to uniquely identify the object.

Example:

metadata:
  name: k0s-cluster-name

Spec Fields

spec.hosts <sequence> (required)

A list of cluster hosts. Host requirements:

• Currently only linux targets are supported
• The user must either be root or have passwordless sudo access.
• The host must fulfill the k0s system requirements

See host object documentation below.

spec.k0s <mapping> (optional)

Settings related to the k0s cluster.

See k0s object documentation below.

Host Fields

spec.hosts[*].role <string> (required)

One of:

• controller - a controller host
• controller+worker - a controller host that will also run workloads
• single - a single-node cluster host, the configuration can only contain one host
• worker - a worker host

spec.hosts[*].noTaints <boolean> (optional) (default: false)

When true and used in conjuction with the controller+worker role, the default taints are disabled making regular workloads schedulable on the node. By default, k0s sets a node-role.kubernetes.io/master:NoSchedule taint on controller+worker nodes and only workloads with toleration for it will be scheduled.

spec.hosts[*].uploadBinary <boolean> (optional) (default: false)

When true, the k0s binaries for target host will be downloaded and cached on the local host and uploaded to the target. When false, the k0s binary downloading is performed on the target host itself

spec.hosts[*].k0sBinaryPath <string> (optional)

A path to a file on the local host that contains a k0s binary to be uploaded to the host. Can be used to test drive a custom development build of k0s.

spec.hosts[*].k0sDownloadURL <string> (optional)

A URL to download the k0s binary from. The default is to download from the k0s repository. The URL can contain '%'-prefixed tokens that will be replaced with the host's information, see tokens.

spec.hosts[*].hostname <string> (optional)

Override host's hostname. When not set, the hostname reported by the operating system is used.

spec.hosts[*].dataDir <string> (optional) (default: /var/lib/k0s)

Set host's k0s data-dir.

spec.hosts[*].installFlags <sequence> (optional)

Extra flags passed to the k0s install command on the target host. See k0s install --help for a list of options.

spec.hosts[*].environment <mapping> (optional)

List of key-value pairs to set to the target host's environment variables.

Example:

environment:
  HTTP_PROXY: 10.0.0.1:443

spec.hosts[*].files <sequence> (optional)

List of files to be uploaded to the host.

Example:

- name: image-bundle
  src: airgap-images.tgz
  dstDir: /var/lib/k0s/images/
  perm: 0600

• name: name of the file "bundle", used only for logging purposes (optional)
• src: File path, an URL or Glob pattern to match files to be uploaded. URL sources will be directly downloaded using the target host. If the value is a URL, '%'-prefixed tokens can be used, see tokens. (required)
• dstDir: Destination directory for the file(s). k0sctl will create full directory structure if it does not already exist on the host (default: user home)
• dst: Destination filename for the file. Only usable for single file uploads (default: basename of file)
• perm: File permission mode for uploaded file(s) (default: same as local)
• dirPerm: Directory permission mode for created directories (default: 0755)
• user: User name of file/directory owner, must exist on the host (optional)
• group: Group name of file/directory owner, must exist on the host (optional)

spec.hosts[*].hooks <mapping> (optional)

Run a set of commands on the remote host during k0sctl operations.

Example:

hooks:
  apply:
    before:
      - date >> k0sctl-apply.log
    after:
      - echo "apply success" >> k0sctl-apply.log

The currently available "hook points" are:

• apply: Runs during k0sctl apply
  • before: Runs after configuration and host validation, right before configuring k0s on the host
  • after: Runs before disconnecting from the host after a successful apply operation
• backup: Runs during k0s backup
  • before: Runs before k0sctl runs the k0s backup command
  • after: Runs before disconnecting from the host after successfully taking a backup
• reset: Runs during k0sctl reset
  • before: Runs after gathering information about the cluster, right before starting to remove the k0s installation.
  • after: Runs before disconnecting from the host after a successful reset operation

spec.hosts[*].os <string> (optional) (default: ``)

Override OS distribution auto-detection. By default k0sctl detects the OS by reading /etc/os-release or /usr/lib/os-release files. In case your system is based on e.g. Debian but the OS release info has something else configured you can override k0sctl to use Debian based functionality for the node with:

  - role: worker
    os: debian
    ssh:
      address: 10.0.0.2

spec.hosts[*].privateInterface <string> (optional) (default: ``)

Override private network interface selected by host fact gathering. Useful in case fact gathering picks the wrong private network interface.

  - role: worker
    os: debian
    privateInterface: eth1

spec.hosts[*].privateAddress <string> (optional) (default: ``)

Override private IP address selected by host fact gathering. Useful in case fact gathering picks the wrong IPAddress.

  - role: worker
    os: debian
    privateAddress: 10.0.0.2

spec.hosts[*].ssh <mapping> (optional)

SSH connection options.

Example:

spec:
  hosts:
    - role: controller
      ssh:
        address: 10.0.0.2
        user: ubuntu
        keyPath: ~/.ssh/id_rsa

It's also possible to tunnel connections through a bastion host. The bastion configuration has all the same fields as any SSH connection:

spec:
  hosts:
    - role: controller
      ssh:
        address: 10.0.0.2
        user: ubuntu
        keyPath: ~/.ssh/id_rsa
        bastion:
          address: 10.0.0.1
          user: root
          keyPath: ~/.ssh/id_rsa2

SSH agent and auth forwarding are also supported, a host without a keyfile:

spec:
  hosts:
    - role: controller
      ssh:
        address: 10.0.0.2
        user: ubuntu

$ ssh-add ~/.ssh/aws.pem
$ ssh -A user@jumphost
user@jumphost ~ $ k0sctl apply

Pageant or openssh-agent can be used on Windows.

spec.hosts[*].ssh.address <string> (required)

IP address of the host

spec.hosts[*].ssh.user <string> (optional) (default: root)

Username to log in as.

spec.hosts[*].ssh.port <number> (required)

TCP port of the SSH service on the host.

spec.hosts[*].ssh.keyPath <string> (optional) (default: ~/.ssh/identity ~/.ssh/id_rsa ~/.ssh/id_dsa)

Path to an SSH key file. If a public key is used, ssh-agent is required. When left empty, the default value will first be looked for from the ssh configuration (default ~/.ssh/config) IdentityFile parameter.

spec.hosts[*].localhost <mapping> (optional)

Localhost connection options. Can be used to use the local host running k0sctl as a node in the cluster.

spec.hosts[*].localhost.enabled <boolean> (optional) (default: false)

This must be set true to enable the localhost connection.

spec.hosts[*].openSSH <mapping> (optional)

An alternative SSH client protocol that uses the system's openssh client for connections.

Example:

spec:
  hosts:
    - role: controller
      openSSH:
        address: 10.0.0.2

The only required field is the address and it can also be a hostname that is found in the ssh config. All other options such as user, port and keypath will use the same defaults as if running ssh from the command-line or will use values found from the ssh config.

An example SSH config:

Host controller1
  Hostname 10.0.0.1
  Port 2222
  IdentityFile ~/.ssh/id_cluster_esa

If this is in your ~/.ssh/config, you can simply use the host alias as the address in your k0sctl config:

spec:
  hosts:
    - role: controller
      openSSH:
        address: controller1
        # if the ssh configuration is in a different file, you can use:
        # configPath: /path/to/config

spec.hosts[*].openSSH.address <string> (required)

IP address, hostname or ssh config host alias of the host

spec.hosts[*].openSSH.user <string> (optional)

Username to connect as.

spec.hosts[*].openSSH.port <number> (optional)

Remote port.

spec.hosts[*].openSSH.keyPath <string> (optional)

Path to private key.

spec.hosts[*].openSSH.configPath <string> (optional)

Path to ssh config, defaults to ~/.ssh/config with fallback to /etc/ssh/ssh_config.

spec.hosts[*].openSSH.disableMultiplexing <boolean> (optional)

The default mode of operation is to use connection multiplexing where a ControlMaster connection is opened and the subsequent connections to the same host use the master connection over a socket to communicate to the host.

If this is disabled by setting disableMultiplexing: true, running every remote command will require reconnecting and reauthenticating to the host.

spec.hosts[*].openSSH.options <mapping> (optional)

Additional options as key/value pairs to use when running the ssh client.

Example:

openSSH:
  address: host
  options:
      ForwardAgent: true  # -o ForwardAgent=yes
      StrictHostkeyChecking: false # -o StrictHostkeyChecking: no

spec.hosts[*].reset <boolean> (optional) (default: false)

If set to true k0sctl will remove the node from kubernetes and reset k0s on the host.

K0s Fields

spec.k0s.version <string> (optional) (default: auto-discovery)

The version of k0s to deploy. When left out, k0sctl will default to using the latest released version of k0s or the version already running on the cluster.

spec.k0s.versionChannel <string> (optional) (default: stable)

Possible values are stable and latest.

When spec.k0s.version is left undefined, this setting can be set to latest to allow k0sctl to include k0s pre-releases when looking for the latest version. The default is to only look for stable releases.

spec.k0s.dynamicConfig <boolean> (optional) (default: false)

Enable k0s dynamic config. The setting will be automatically set to true if:

• Any controller node has --enable-dynamic-config in installFlags
• Any existing controller node has --enable-dynamic-config in run arguments (k0s status -o json)

Note: When running k0s in dynamic config mode, k0sctl will ONLY configure the cluster-wide configuration during the first time initialization, after that the configuration has to be managed via k0s config edit or k0sctl config edit. The node specific configuration will be updated on each apply.

See also:

• k0s Dynamic Configuration

spec.k0s.config <mapping> (optional) (default: auto-generated)

Embedded k0s cluster configuration. See k0s configuration documentation for details.

When left out, the output of k0s config create will be used.

Tokens

The following tokens can be used in the k0sDownloadURL and files.[*].src fields:

• %% - literal %
• %p - host architecture (arm, arm64, amd64)
• %v - k0s version (v1.21.0+k0s.0)
• %x - k0s binary extension (currently always empty)

Any other tokens will be output as-is including the % character.

Example:

  - role: controller
    k0sDownloadURL: https://files.example.com/k0s%20files/k0s-%v-%p%x
    # Expands to https://files.example.com/k0s%20files/k0s-v1.21.0+k0s.0-amd64