Overview

This guide provides comprehensive instructions for using Ansible to set up a Kubernetes or OpenShift cluster, automating the process to reduce manual intervention, ensure consistency, and scale easily.

Why Use Ansible for Cluster Management?

Ansible offers the following advantages when managing clusters:

Automation: Reduces manual configuration, speeds up deployment.
Consistency: Ensures all nodes are configured identically.
Scalability: Easily add or remove nodes as needed.
Idempotency: Re-running playbooks does not cause duplicate actions, maintaining the desired state.

Prerequisites

Before proceeding, ensure that:

Ansible is Installed: Install with pip install ansible.
Server Access: Access to multiple servers (either virtual machines or bare-metal) where the Kubernetes/OpenShift nodes will be deployed.
SSH Access: Ensure SSH access is configured for these servers.
Required Packages: Necessary packages, such as curl, docker, and kubelet, are installed on all nodes.
Inventory File: An Ansible inventory file is created to define your cluster nodes.

Step-by-Step Guide to Set Up a Kubernetes Cluster Using Ansible

Step 1: Create the Ansible Inventory File

Create an inventory file named inventory.ini to define the nodes in the Kubernetes cluster.

Example inventory.ini:

[k8s_cluster]
master ansible_host=192.168.1.10
node1 ansible_host=192.168.1.11
node2 ansible_host=192.168.1.12

[k8s_cluster:vars]
ansible_ssh_user=your_user

Step 2: Write the Ansible Playbook

Create an Ansible playbook called k8s-setup.yml with tasks to install and configure Kubernetes components.

Sample `k8s-setup.yml`

---
- name: Set up Kubernetes Cluster
  hosts: k8s_cluster
  become: true
  tasks:

    - name: Install required packages
      apt:
        name:
          - apt-transport-https
          - ca-certificates
          - curl
          - software-properties-common
        state: present

    - name: Add Docker GPG key
      apt_key:
        url: https://download.docker.com/linux/ubuntu/gpg
        state: present

    - name: Add Docker repository
      apt_repository:
        repo: deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable
        state: present

    - name: Install Docker
      apt:
        name: docker-ce
        state: latest

    - name: Enable and start Docker
      service:
        name: docker
        state: started
        enabled: true

    - name: Install Kubernetes components
      apt:
        name:
          - kubelet
          - kubeadm
          - kubectl
        state: latest

    - name: Disable swap (required for Kubernetes)
      command: swapoff -a
      when: ansible_os_family == "Debian"

    - name: Initialize Kubernetes master
      command: kubeadm init --pod-network-cidr=10.244.0.0/16
      when: inventory_hostname == "master"
      register: k8s_init
      ignore_errors: true

    - name: Copy Kubernetes admin config to user home
      command: "{{ item }}"
      with_items:
        - mkdir -p $HOME/.kube
        - cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
        - chown $(id -u):$(id -g) $HOME/.kube/config
      when: inventory_hostname == "master"

    - name: Install Flannel network plugin
      command: kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/k8s-manifests/kube-flannel.yml
      when: inventory_hostname == "master"

    - name: Join worker nodes to the cluster
      command: "{{ hostvars['master']['k8s_init']['stdout_lines'][-1] }}"
      when: inventory_hostname != "master"

Explanation of the Playbook Tasks

Install Required Packages: Installs essential packages like apt-transport-https, curl, and ca-certificates.
Docker Installation: Adds the Docker GPG key and repository, installs Docker, and enables the Docker service.
Install Kubernetes Components: Installs kubelet, kubeadm, and kubectl.
Disable Swap: Kubernetes requires that swap be disabled on all nodes.
Initialize Kubernetes Master Node: Runs kubeadm init on the master node, using a specified Pod network CIDR for Flannel.
Copy Kubernetes Config to Admin Directory: Copies the Kubernetes configuration to the user’s home directory on the master node.
Install Flannel Network Plugin: Applies Flannel network configuration to the cluster.
Join Worker Nodes: Executes the join command on worker nodes using the command output from the master’s initialization.

Step 3: Run the Ansible Playbook

To execute the playbook and set up your cluster, run:

ansible-playbook -i inventory.ini k8s-setup.yml

This will connect to the specified hosts in your inventory and complete the setup of a Kubernetes cluster.

Step 4: Verify the Cluster

To verify your Kubernetes cluster, run the following command on the master node:

kubectl get nodes

This command should list all nodes in the cluster, showing them in a “Ready” state.

Customizing for OpenShift Clusters

For OpenShift clusters, use the OpenShift Ansible Installer and make modifications to the playbook, such as adjusting for specific OpenShift requirements and using the appropriate OpenShift commands.

Benefits of Using Ansible for Cluster Management

Consistency: Ensures that each node is configured identically every time.
Automation: Reduces repetitive tasks, allowing for fast deployment and updates.
Scalability: Easily modify the inventory and add or remove nodes as needed.
Integration: Seamlessly integrates with other infrastructure automation workflows, making it easier to manage Kubernetes/OpenShift clusters alongside other infrastructure.

Conclusion

Using Ansible to set up and manage Kubernetes or OpenShift clusters simplifies deployment, minimizes human error, and creates a scalable, consistent environment.

Kubernetes Cluster Setup Using Ansible