Ansible

Why Ansible?

K3s cluster creation requires knowing server node IPs to connect other nodes. Since my router assigns IPs dynamically via DHCP, I can't hardcode them in cloud-init config.

The solution: Terraform process generates an inventory.yml with node IPs, then Ansible uses this to install and configure k3s.

Alternative Approach

A simpler alternative would be configuring a static IP for the first server node and referencing it in cloud-init configs for other nodes to join the cluster. This approach would eliminate the need for Ansible.

TODO: Test this approach.

Install

I use pipx to install Ansible.

# install pipx
sudo apt install -y pipx
pipx ensurepath

# install ansible
pipx install --include-deps ansible

Deployment

Required Files

1. inventory.yml - Generated by Terraform with node IPs and k3s token.
2. playbook.yml - Defines k3s installation and copying config file to local ~/.kube/config.

# inventory.yml
all:
  hosts:
  %{~ for name, details in nodes ~}
    ${name}:
      ansible_host: ${details.ip}
  %{~ endfor ~}
  vars:
    k3s_token: ${k3s_token}

k3s_servers:
  hosts:
  %{~ for name, details in nodes ~}
  %{~ if details.role == "server" ~}
    ${name}:
  %{~ endif ~}
  %{~ endfor ~}

k3s_agents:
  hosts:
  %{~ for name, details in nodes ~}
  %{~ if details.role == "agent" ~}
    ${name}:
  %{~ endif ~}
  %{~ endfor ~}

# playbook.yml
- hosts: k3s_servers
  tasks:
    - name: Install K3S server
      shell: >
        curl -sfL https://get.k3s.io |
        sh -s - server --cluster-init
        --disable servicelb
        --kube-proxy-arg proxy-mode=ipvs
        --kube-proxy-arg ipvs-strict-arp
      environment:
        K3S_TOKEN: '{{ k3s_token }}'
      args:
        creates: /usr/local/bin/k3s

- hosts: k3s_servers[0]
  vars:
    k3s_server: "{{ groups['k3s_servers'][0] }}"
    k3s_url: "https://{{ hostvars[k3s_server]['ansible_host'] }}:6443"
  tasks:
    - name: Display K3S config
      shell: k3s kubectl config view --raw
      become: true
      register: config_output
    - name: Update server URL in config
      set_fact:
        updated_config: "{{ config_output.stdout | regex_replace('server: .*', 'server: ' + k3s_url) }}"
    - name: Copy K3S config to local.
      copy:
        content: '{{ updated_config }}'
        dest: '/home/viet/.kube/config'
      delegate_to: localhost

- hosts: k3s_agents
  vars:
    k3s_server: "{{ groups['k3s_servers'][0] }}"
    k3s_url: "https://{{ hostvars[k3s_server]['ansible_host'] }}:6443"
  tasks:
    - name: Install K3S agent
      shell: >
        curl -sfL https://get.k3s.io |
        sh -s - agent
      environment:
        K3S_TOKEN: '{{ k3s_token }}'
        K3S_URL: '{{ k3s_url }}'
      args:
        creates: /usr/local/bin/k3s

Execution

ANSIBLE_HOST_KEY_CHECKING=False is needed to avoid typing yes when Ansible connecting to the VM for the first time.

ANSIBLE_HOST_KEY_CHECKING=False ansible-playbook -i inventory.yml playbook.yml