Question: How do you automate the deployment of a MongoDB cluster using Ansible?

Answer

To automate the deployment of a MongoDB cluster using Ansible, you need to understand both MongoDB and Ansible. MongoDB is a NoSQL database that offers high performance, high availability, and easy scalability. Ansible, on the other hand, is an open-source IT automation tool used to automate applications' configuration, provisioning, deployment, and many other IT needs.

1. Installing Ansible

You must have Ansible installed on your control machine (the machine from which you will run your playbooks). You can install Ansible using your package manager of choice:

# For Ubuntu/Debian:
sudo apt update && sudo apt install ansible

# For CentOS/RHEL:
sudo yum install ansible

2. Creating Ansible Playbook for MongoDB Cluster Deployment

An Ansible playbook is a YAML file where you define what actions should take place in your managed nodes (in this case, MongoDB cluster nodes).

Here's a basic example of a playbook (mongodb_cluster.yml) that installs MongoDB on multiple servers, configures replicaset, and sets up authentication. Note: This is a simplified example to get you started. In real-world usage, you would need to consider security, backups, monitoring, and more detailed configurations.

---
- hosts: mongodb_servers
  become: true
  vars:
    mongodb_version: '4.4'
    mongodb_user: 'mongoAdmin'
    mongodb_password: 'YourSecurePassword'
  tasks:
  - name: Import the MongoDB public key
    ansible.builtin.apt_key:
      url: https://www.mongodb.org/static/pgp/server-{{ mongodb_version }}.asc
      state: present

  - name: Add the MongoDB repository
    ansible.builtin.apt_repository:
      repo: deb http://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/{{ mongodb_version }} multiverse
      state: present
      update_cache: yes

  - name: Install MongoDB packages
    ansible.builtin.apt:
      name: mongodb-org
      state: present

  - name: Start and enable MongoDB service
    ansible.builtin.service:
      name: mongod
      state: started
      enabled: yes

  - name: Wait for MongoDB to start
    ansible.builtin.wait_for:
      port: 27017
      delay: 5

  - name: Create admin user
    community.mongodb.mongodb_shell:
      login_database: admin
      eval: "db.createUser({user: '{{ mongodb_user }}', pwd: '{{ mongodb_password }}', roles:[{role:'root',db:'admin'}]});"
    run_once: true

  # Additional tasks to configure replica set and shardings can be added here.

3. Running Your Playbook

With your inventory file (hosts.ini) listing all the target MongoDB servers under [mongodb_servers], you can run your playbook using the following command:

ansible-playbook -i hosts.ini mongodb_cluster.yml

Conclusion

This guide provided a basic introduction to automating the deployment of a MongoDB cluster using Ansible. Keep in mind, for production environments, you'll need to secure your MongoDB cluster by enabling authentication, setting up TLS/SSL, configuring firewalls, among others.

Automating with Ansible not only simplifies the initial setup but also ensures consistency across your environment, making it easier to scale, manage, and maintain your MongoDB cluster over time.