Ansible

Ansible is an agentless IT automation platform that uses SSH (Linux) or WinRM (Windows) to configure systems, deploy software, and orchestrate workflows. Written in Python, maintained by Red Hat.

Core concepts:

• Inventory: list of managed hosts, grouped by role or environment (INI or YAML format)
• Playbook: YAML file containing ordered lists of tasks to execute on specified hosts
• Task: a single action using a module (e.g., install a package, copy a file, restart a service)
• Module: reusable unit of work (1000+ built-in: apt, yum, copy, template, service, docker_container)
• Role: reusable, self-contained collection of tasks, templates, files, and variables (similar to a library)
• Facts: system information automatically gathered from managed hosts (OS, IP, CPU, memory)

Key properties:

• Agentless: no software installed on managed nodes; uses SSH
• Idempotent: running a playbook multiple times produces the same result. Ansible checks current state before making changes.
• Declarative: you describe the desired state, not the steps to get there
• Push-based: the control node pushes configuration to managed nodes (vs. pull-based tools like Puppet/Chef)

Ansible vs. alternatives:

Tool	Agent	Language	Approach
Ansible	No (SSH)	YAML	Push, declarative
Terraform	No (API)	HCL	Push, declarative (infrastructure)
Puppet	Yes	Ruby DSL	Pull, declarative
Chef	Yes	Ruby DSL	Pull, imperative

# inventory.yml
all:
  children:
    webservers:
      hosts:
        web-01: { ansible_host: 10.0.1.10 }
        web-02: { ansible_host: 10.0.1.11 }
    databases:
      hosts:
        db-01: { ansible_host: 10.0.2.10 }

# playbook.yml
- name: Configure web servers
  hosts: webservers
  become: true
  tasks:
    - name: Install Nginx
      apt:
        name: nginx
        state: present
        update_cache: true

    - name: Deploy site config
      template:
        src: templates/nginx.conf.j2
        dest: /etc/nginx/sites-available/default
      notify: Restart Nginx

    - name: Ensure Nginx is running
      service:
        name: nginx
        state: started
        enabled: true

  handlers:
    - name: Restart Nginx
      service:
        name: nginx
        state: restarted

# Run the playbook
$ ansible-playbook -i inventory.yml playbook.yml
PLAY [Configure web servers] *****
TASK [Install Nginx] *************
changed: [web-01]
changed: [web-02]
TASK [Deploy site config] ********
changed: [web-01]
changed: [web-02]
PLAY RECAP ***********************
web-01: ok=3  changed=2  failed=0
web-02: ok=3  changed=2  failed=0