Ansible Role: k3s (v3.x)

Ansible role for installing K3S (“Lightweight
Kubernetes”) as either a standalone server or cluster.

Help Wanted!

Hi! @xanmanning is looking for a new
maintainer to work on this Ansible role. This is because I don’t have as much
free time any more and I no longer write Ansible regularly as part of my day
job. If you’re interested, get in touch.

Release notes

Please see Releases
and CHANGELOG.md.

Requirements

The host you’re running Ansible from requires the following Python dependencies:

• python >= 3.6.0 - See Notes below.
• ansible >= 2.9.16 or ansible-base >= 2.10.4

You can install dependencies using the requirements.txt file in this repository:
pip3 install -r requirements.txt.

This role has been tested against the following Linux Distributions:

• Alpine Linux
• Amazon Linux 2
• Archlinux
• CentOS 8
• Debian 11
• Fedora 31
• Fedora 32
• Fedora 33
• openSUSE Leap 15
• RockyLinux 8
• Ubuntu 20.04 LTS

The v3 releases of this role only supports k3s >= v1.19, for
k3s < v1.19 please consider updating or use the v1.x releases of this role.

Before upgrading, see CHANGELOG for notifications of breaking
changes.

Role Variables

Since K3s v1.19.1+k3s1
you can now configure K3s using a
configuration file
rather than environment variables or command line arguments. The v2 release of
this role has moved to the configuration file method rather than populating a
systemd unit file with command-line arguments. There may be exceptions that are
defined in Global/Cluster Variables, however you will
mostly be configuring k3s by configuration files using the k3s_server and
k3s_agent variables.

See “Server (Control Plane) Configuration“ and “Agent (Worker) Configuraion“
below.

Global/Cluster Variables

Below are variables that are set against all of the play hosts for environment
consistency. These are generally cluster-level configuration.

K3S Service Configuration

The below variables change how and when the systemd service unit file for K3S
is run. Use this with caution, please refer to the systemd documentation
for more information.

* The systemd unit template always specifies network-online.target for
wants and after.

** The file must already exist on the target host, this role will not create
nor manage the file. You can manage this file outside of the role with
pre-tasks in your Ansible playbook.

Group/Host Variables

Below are variables that are set against individual or groups of play hosts.
Typically you’d set these at group level for the control plane or worker nodes.

Server (Control Plane) Configuration

The control plane is configured with the k3s_server dict variable. Please
refer to the below documentation for configuration options:

https://rancher.com/docs/k3s/latest/en/installation/install-options/server-config/

The k3s_server dictionary variable will contain flags from the above
(removing the -- prefix). Below is an example:

k3s_server:
  datastore-endpoint: postgres://postgres:verybadpass@database:5432/postgres?sslmode=disable
  cluster-cidr: 172.20.0.0/16
  flannel-backend: 'none'  # This needs to be in quotes
  disable:
    - traefik
    - coredns

Alternatively, you can create a .yaml file and read it in to the k3s_server
variable as per the below example:

k3s_server: "{{ lookup('file', 'path/to/k3s_server.yml') | from_yaml }}"

Check out the Documentation for example
configuration.

Agent (Worker) Configuration

Workers are configured with the k3s_agent dict variable. Please refer to the
below documentation for configuration options:

https://rancher.com/docs/k3s/latest/en/installation/install-options/agent-config

The k3s_agent dictionary variable will contain flags from the above
(removing the -- prefix). Below is an example:

k3s_agent:
  with-node-id: true
  node-label:
    - "foo=bar"
    - "hello=world"

Alternatively, you can create a .yaml file and read it in to the k3s_agent
variable as per the below example:

k3s_agent: "{{ lookup('file', 'path/to/k3s_agent.yml') | from_yaml }}"

Check out the Documentation for example
configuration.

Ansible Controller Configuration Variables

The below variables are used to change the way the role executes in Ansible,
particularly with regards to privilege escalation.

Important note about Python

From v3 of this role, Python 3 is required on the target system as well as on
the Ansible controller. This is to ensure consistent behaviour for Ansible
tasks as Python 2 is now EOL.

If target systems have both Python 2 and Python 3 installed, it is most likely
that Python 2 will be selected by default. To ensure Python 3 is used on a
target with both versions of Python, ensure ansible_python_interpreter is
set in your inventory. Below is an example inventory:

---
k3s_cluster:
  hosts:
    kube-0:
      ansible_user: ansible
      ansible_host: 10.10.9.2
      ansible_python_interpreter: /usr/bin/python3
    kube-1:
      ansible_user: ansible
      ansible_host: 10.10.9.3
      ansible_python_interpreter: /usr/bin/python3
    kube-2:
      ansible_user: ansible
      ansible_host: 10.10.9.4
      ansible_python_interpreter: /usr/bin/python3

Important note about k3s_release_version

If you do not set a k3s_release_version the latest version from the stable
channel of k3s will be installed. If you are developing against a specific
version of k3s you must ensure this is set in your Ansible configuration, eg:

k3s_release_version: v1.19.3+k3s1

It is also possible to install specific K3s “Channels”, below are some
examples for k3s_release_version:

k3s_release_version: false             # defaults to 'stable' channel
k3s_release_version: stable            # latest 'stable' release
k3s_release_version: testing           # latest 'testing' release
k3s_release_version: v1.19             # latest 'v1.19' release
k3s_release_version: v1.19.3+k3s3      # specific release
# Specific commit
# CAUTION - only used for testing - must be 40 characters
k3s_release_version: 48ed47c4a3e420fa71c18b2ec97f13dc0659778b

Important note about k3s_install_hard_links

If you are using the system-upgrade-controller
you will need to use hard links rather than symbolic links as the controller
will not be able to follow symbolic links. This option has been added however
is not enabled by default to avoid breaking existing installations.

To enable the use of hard links, ensure k3s_install_hard_links is set
to true.

k3s_install_hard_links: true

The result of this can be seen by running the following in k3s_install_dir:

ls -larthi | grep -E 'k3s|ctr|ctl' | grep -vE ".sh$" | sort

Symbolic Links:

[root@node1 bin]# ls -larthi | grep -E 'k3s|ctr|ctl' | grep -vE ".sh$" | sort
3277823 -rwxr-xr-x 1 root root  52M Jul 25 12:50 k3s-v1.18.4+k3s1
3279565 lrwxrwxrwx 1 root root   31 Jul 25 12:52 k3s -> /usr/local/bin/k3s-v1.18.6+k3s1
3279644 -rwxr-xr-x 1 root root  51M Jul 25 12:52 k3s-v1.18.6+k3s1
3280079 lrwxrwxrwx 1 root root   31 Jul 25 12:52 ctr -> /usr/local/bin/k3s-v1.18.6+k3s1
3280080 lrwxrwxrwx 1 root root   31 Jul 25 12:52 crictl -> /usr/local/bin/k3s-v1.18.6+k3s1
3280081 lrwxrwxrwx 1 root root   31 Jul 25 12:52 kubectl -> /usr/local/bin/k3s-v1.18.6+k3s1

Hard Links:

[root@node1 bin]# ls -larthi | grep -E 'k3s|ctr|ctl' | grep -vE ".sh$" | sort
3277823 -rwxr-xr-x 1 root root  52M Jul 25 12:50 k3s-v1.18.4+k3s1
3279644 -rwxr-xr-x 5 root root  51M Jul 25 12:52 crictl
3279644 -rwxr-xr-x 5 root root  51M Jul 25 12:52 ctr
3279644 -rwxr-xr-x 5 root root  51M Jul 25 12:52 k3s
3279644 -rwxr-xr-x 5 root root  51M Jul 25 12:52 k3s-v1.18.6+k3s1
3279644 -rwxr-xr-x 5 root root  51M Jul 25 12:52 kubectl

Important note about k3s_build_cluster

If you set k3s_build_cluster to false, this role will install each play
host as a standalone node. An example of when you might use this would be
when building a large number of standalone IoT devices running K3s. Below is a
hypothetical situation where we are to deploy 25 Raspberry Pi devices, each a
standalone system and not a cluster of 25 nodes. To do this we’d use a playbook
similar to the below:

- hosts: k3s_nodes  # eg. 25 RPi's defined in our inventory.
  vars:
    k3s_build_cluster: false
  roles:
     - xanmanning.k3s

Important note about k3s_control_node and High Availability (HA)

By default only one host will be defined as a control node by Ansible, If you
do not set a host as a control node, this role will automatically delegate
the first play host as a control node. This is not suitable for use within
a Production workload.

If multiple hosts have k3s_control_node set to true, you must also set
datastore-endpoint in k3s_server as the connection string to a MySQL or
PostgreSQL database, or external Etcd cluster else the play will fail.

If using TLS, the CA, Certificate and Key need to already be available on
the play hosts.

See: High Availability with an External DB

It is also possible, though not supported, to run a single K3s control node
with a datastore-endpoint defined. As this is not a typically supported
configuration you will need to set k3s_use_unsupported_config to true.

Since K3s v1.19.1 it is possible to use an embedded Etcd as the backend
database, and this is done by setting k3s_etcd_datastore to true.
The best practice for Etcd is to define at least 3 members to ensure quorum is
established. In addition to this, an odd number of members is recommended to
ensure a majority in the event of a network partition. If you want to use 2
members or an even number of members, please set k3s_use_unsupported_config
to true.

Important note about k3s_server_manifests_urls and k3s_server_pod_manifests_urls

To deploy server manifests and server pod manifests from URL, you need to
specify a url and optionally a filename (if none provided basename is used). Below is an example of how to deploy the
Tigera operator for Calico and kube-vip.

---
k3s_server_manifests_urls:
  - url: https://docs.projectcalico.org/archive/v3.19/manifests/tigera-operator.yaml
    filename: tigera-operator.yaml
k3s_server_pod_manifests_urls:
  - url: https://raw.githubusercontent.com/kube-vip/kube-vip/main/example/deploy/0.1.4.yaml
    filename: kube-vip.yaml

Important note about k3s_airgap

When deploying k3s in an air gapped environment you should provide the k3s binary in ./files/. The binary will not be downloaded from Github and will subsequently not be verified using the provided sha256 sum, nor able to verify the version that you are running. All risks and burdens associated are assumed by the user in this scenario.

Dependencies

No dependencies on other roles.

Example Playbooks

Example playbook, single control node running testing channel k3s:

- hosts: k3s_nodes
  vars:
    k3s_release_version: testing
  roles:
     - role: xanmanning.k3s

Example playbook, Highly Available with PostgreSQL database running the latest
stable release:

- hosts: k3s_nodes
  vars:
    k3s_registration_address: loadbalancer  # Typically a load balancer.
    k3s_server:
      datastore-endpoint: "postgres://postgres:verybadpass@database:5432/postgres?sslmode=disable"
  pre_tasks:
    - name: Set each node to be a control node
      ansible.builtin.set_fact:
        k3s_control_node: true
      when: inventory_hostname in ['node2', 'node3']
  roles:
    - role: xanmanning.k3s

License

BSD 3-clause

Contributors

Contributions from the community are very welcome, but please read the
contribution guidelines before doing so, this will help
make things as streamlined as possible.

Also, please check out the awesome
list of contributors.

Author Information

Xan Manning