Introduction to Ansible — Automate Infrastructure Without an Agent

Before configuration management tools, sysadmins maintained hundreds of servers by hand — logging in, running commands, hoping nothing went wrong. This was error-prone, slow, and impossible to scale. Ansible was built to solve exactly this problem.

What makes Ansible different from Chef and Puppet is that it's agentless. No daemon running on your servers, no certificates to manage, no port to open beyond SSH. Ansible runs from your machine, connects over SSH, executes tasks, and disconnects.

By the end of this article you'll understand Ansible's core concepts — inventory, playbooks, tasks, and modules — and you'll have a working playbook that installs and configures Nginx on a remote server.

Inventory, Playbooks, and Modules — The Three Core Concepts

Ansible has three building blocks. The inventory is a list of servers you want to manage — IP addresses or hostnames, organised into groups. A playbook is a YAML file describing what to do on which servers. A module is a pre-built unit of work — install a package, copy a file, start a service. Ansible ships with thousands of modules covering everything from AWS to Windows registry.

# inventory.ini — tell Ansible which servers exist
[webservers]
192.168.1.10  ansible_user=ubuntu  ansible_ssh_private_key_file=~/.ssh/id_rsa
192.168.1.11  ansible_user=ubuntu

[databases]
192.168.1.20  ansible_user=ubuntu

[production:children]  # Group of groups
webservers
databases

Your First Playbook

A playbook is a list of plays. Each play targets a group of servers and runs a list of tasks. Each task calls one Ansible module. The order is: playbook → plays → tasks → modules. Ansible executes tasks top-to-bottom, on all targeted servers in parallel.

---
- name: Configure web servers  # Play name — describes intent
  hosts: webservers             # Target the webservers group from inventory
  become: true                  # Use sudo for privileged operations

  tasks:
    - name: Update apt package cache
      apt:
        update_cache: yes
        cache_valid_time: 3600  # Only update if cache is older than 1 hour

    - name: Install Nginx
      apt:
        name: nginx
        state: present          # 'present' = install, 'absent' = remove, 'latest' = upgrade

    - name: Copy custom Nginx config
      copy:
        src: files/nginx.conf   # File on your local machine
        dest: /etc/nginx/nginx.conf
        owner: root
        group: root
        mode: '0644'
      notify: Restart Nginx     # Trigger handler only if this task changes something

    - name: Ensure Nginx is running and starts on boot
      service:
        name: nginx
        state: started
        enabled: yes

  handlers:  # Only run when notified, and only once even if notified multiple times
    - name: Restart Nginx
      service:
        name: nginx
        state: restarted