Introduction to Ansible

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Chapter objectives

• Understand what Ansible is
• Discover the fundamental concepts
• Compare Ansible to other tools
• Identify use cases

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1 - What is Ansible?

Definition

Ansible is an open-source IT automation tool that allows you to:

• Configure servers
• Deploy applications
• Orchestrate workflows
• Manage infrastructure as code

Key characteristics

Why "Agentless"?

With Agent	Without Agent (Ansible)
Agent to install on each server	Standard SSH connection
Agent maintenance	Nothing to maintain
Resource consumption	No overhead
Additional ports	SSH port only

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2 - Ansible architecture

Overview

Components

Component	Description
Control Node	Machine where Ansible is installed
Managed Nodes	Servers managed by Ansible
Inventory	List of hosts to manage
Playbook	YAML file describing the tasks
Module	Unit of work (e.g. apt, copy, file)
Role	Organized collection of playbooks

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3 - Fundamental concepts

Idempotence

Idempotence guarantees that a task produces the same result, whether it is run 1 or 100 times.

Example:

# Cette tâche installe nginx SI il n'est pas déjà installé
- name: Installer nginx
  apt:
    name: nginx
    state: present

• 1st run: nginx installed ✅
• 2nd run: "ok" (nothing to do)

Declarative vs Imperative

With Ansible, you describe the desired final state, not the steps to reach it.

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4 - Ansible workflow

Execution flow

Task states

State	Color	Meaning
ok	🟢 Green	Task succeeded, no change
changed	🟡 Yellow	Task succeeded, change made
failed	🔴 Red	Task failed
skipped	🔵 Cyan	Task skipped (condition not met)
unreachable	🔴 Red	Host unreachable

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5 - Use cases

Configuration Management

• Package installation
• Service configuration
• User management
• File deployment

Application Deployment

Cloud Provisioning

Orchestration

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6 - Comparison with other tools

Ansible vs others

Criterion	Ansible	Puppet	Chef	Terraform
Type	Push	Pull	Pull	Push
Agent	No	Yes	Yes	No
Language	YAML	DSL	Ruby	HCL
Curve	Easy	Medium	Hard	Medium
Focus	Config	Config	Config	Infra

When to use Ansible?

Use case	Ansible	Alternative
Server config	✅ Excellent	-
App deployment	✅ Excellent	-
Cloud provisioning	✅ Good	Terraform (better)
K8s orchestration	⚠️ Possible	Helm, ArgoCD
CI/CD	⚠️ Possible	Jenkins, GitLab CI

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7 - Ansible ecosystem

Red Hat products

Product	Description	License
Ansible Core	Automation engine	Open Source
Ansible Galaxy	Community role hub	Free
AWX	Web interface	Open Source
Automation Platform	Enterprise solution	Commercial

Popular modules

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8 - First example

Structure of a playbook

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# site.yml - Mon premier playbook
- name: Configuration serveurs web
  hosts: webservers
  become: yes
  
  tasks:
    - name: Mettre à jour le cache apt
      apt:
        update_cache: yes
    
    - name: Installer nginx
      apt:
        name: nginx
        state: present
    
    - name: Démarrer nginx
      service:
        name: nginx
        state: started
        enabled: yes
    
    - name: Copier la page d'accueil
      copy:
        src: index.html
        dest: /var/www/html/index.html

Execution

# Exécuter le playbook
ansible-playbook -i inventory.ini site.yml

# Résultat
PLAY [Configuration serveurs web] ****

TASK [Mettre à jour le cache apt] ****
ok: [web-01]
ok: [web-02]

TASK [Installer nginx] ****
changed: [web-01]
changed: [web-02]

TASK [Démarrer nginx] ****
changed: [web-01]
changed: [web-02]

PLAY RECAP ****
web-01  : ok=4  changed=2  failed=0
web-02  : ok=4  changed=2  failed=0

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Summary

Key points

• Ansible is agentless: it uses SSH
• Playbooks are in YAML: readable by everyone
• Idempotence guarantees safe executions
• Push-based: you control when to run

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Practical exercises

1. Explain the difference between agentless and agent-based
2. What is idempotence and why is it important?
3. List 3 use cases of Ansible in your context
4. Compare Ansible and Terraform: when to use each?

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