Ansible Expert

Ansible Expert

Expert guidance for Ansible - configuration management, application deployment, and IT automation using declarative YAML playbooks.

Core Concepts

Ansible Architecture

• Control node (runs Ansible)
• Managed nodes (target systems)
• Inventory (hosts and groups)
• Playbooks (YAML automation scripts)
• Modules (units of work)
• Roles (reusable automation units)
• Plugins (extend functionality)

Key Features

• Agentless (SSH-based)
• Idempotent operations
• Declarative syntax
• Human-readable YAML
• Extensible with modules
• Push-based configuration
• Parallel execution

Use Cases

• Configuration management
• Application deployment
• Provisioning
• Continuous delivery
• Security automation
• Orchestration

Installation

# Using pip
pip install ansible

# Using apt (Ubuntu/Debian)
sudo apt update
sudo apt install ansible

# Using yum (RHEL/CentOS)
sudo yum install ansible

# Verify installation
ansible --version

Inventory

Basic Inventory (INI format)

# inventory/hosts
[webservers]
web1.example.com
web2.example.com ansible_host=192.168.1.10

[databases]
db1.example.com ansible_user=dbadmin
db2.example.com

[production:children]
webservers
databases

[production:vars]
ansible_python_interpreter=/usr/bin/python3
ansible_connection=ssh

YAML Inventory

# inventory/hosts.yml
all:
  children:
    webservers:
      hosts:
        web1.example.com:
        web2.example.com:
          ansible_host: 192.168.1.10
    databases:
      hosts:
        db1.example.com:
          ansible_user: dbadmin
        db2.example.com:
    production:
      children:
        webservers:
        databases:
      vars:
        ansible_python_interpreter: /usr/bin/python3
        ansible_connection: ssh

Dynamic Inventory

#!/usr/bin/env python3
# inventory/aws_ec2.py
import json
import boto3

def get_inventory():
    ec2 = boto3.client('ec2', region_name='us-east-1')
    response = ec2.describe_instances(Filters=[
        {'Name': 'instance-state-name', 'Values': ['running']}
    ])

    inventory = {
        '_meta': {'hostvars': {}},
        'all': {'hosts': []},
        'webservers': {'hosts': []},
        'databases': {'hosts': []},
    }

    for reservation in response['Reservations']:
        for instance in reservation['Instances']:
            ip = instance['PrivateIpAddress']
            tags = {tag['Key']: tag['Value'] for tag in instance.get('Tags', [])}

            inventory['all']['hosts'].append(ip)
            inventory['_meta']['hostvars'][ip] = {
                'ansible_host': ip,
                'instance_id': instance['InstanceId'],
                'instance_type': instance['InstanceType'],
            }

            # Group by role tag
            role = tags.get('Role', '')
            if role in inventory:
                inventory[role]['hosts'].append(ip)

    return inventory

if __name__ == '__main__':
    print(json.dumps(get_inventory(), indent=2))

Templates (Jinja2)

{# templates/app.conf.j2 #}
# Application configuration for {{ app_name }}
# Generated by Ansible on {{ ansible_date_time.iso8601 }}

[server]
host = {{ ansible_default_ipv4.address }}
port = {{ app_port }}
workers = {{ ansible_processor_vcpus }}

[database]
host = {{ db_host }}
port = {{ db_port }}
name = {{ db_name }}
user = {{ db_user }}
password = {{ db_password }}

[cache]
enabled = {{ cache_enabled | default(true) | lower }}
{% if cache_enabled | default(true) %}
backend = redis
redis_host = {{ redis_host }}
redis_port = {{ redis_port }}
{% endif %}

[features]
{% for feature, enabled in features.items() %}
{{ feature }} = {{ enabled | lower }}
{% endfor %}

{% if environment == 'production' %}
[production]
debug = false
log_level = warning
{% else %}
[development]
debug = true
log_level = debug
{% endif %}

Variables and Facts

Variable Precedence (low to high)

1. Role defaults
2. Inventory file/script group vars
3. Inventory group_vars/all
4. Playbook group_vars/all
5. Inventory group_vars/\*
6. Playbook group_vars/\*
7. Inventory file/script host vars
8. Inventory host_vars/\*
9. Playbook host_vars/\*
10. Host facts
11. Play vars
12. Play vars_prompt
13. Play vars_files
14. Role vars
15. Block vars
16. Task vars
17. Extra vars (-e flag)

Using Variables

---
- name: Variable examples
  hosts: all
  vars:
    app_name: myapp
    app_version: 1.0.0
  vars_files:
    - vars/common.yml
    - 'vars/{{ environment }}.yml'

  tasks:
    - name: Load variables from file
      include_vars:
        file: 'vars/{{ ansible_distribution }}.yml'

    - name: Set fact
      set_fact:
        full_app_name: '{{ app_name }}-{{ app_version }}'

    - name: Register output
      command: hostname
      register: hostname_output

    - name: Use registered variable
      debug:
        msg: 'Hostname is {{ hostname_output.stdout }}'

    - name: Access facts
      debug:
        msg: |
          OS: {{ ansible_distribution }} {{ ansible_distribution_version }}
          Kernel: {{ ansible_kernel }}
          CPU: {{ ansible_processor_vcpus }} cores
          Memory: {{ ansible_memtotal_mb }} MB
          IP: {{ ansible_default_ipv4.address }}

Error Handling

---
- name: Error handling examples
  hosts: all
  tasks:
    - name: Task that might fail
      command: /bin/false
      ignore_errors: yes

    - name: Task with custom error handling
      block:
        - name: Try to start service
          systemd:
            name: myapp
            state: started
      rescue:
        - name: Log error
          debug:
            msg: 'Failed to start myapp'

        - name: Try alternative
          systemd:
            name: myapp-fallback
            state: started
      always:
        - name: This always runs
          debug:
            msg: 'Cleanup task'

    - name: Assert condition
      assert:
        that:
          - ansible_memtotal_mb >= 2048
          - ansible_processor_vcpus >= 2
        fail_msg: 'Server does not meet minimum requirements'

    - name: Fail when condition
      fail:
        msg: 'Production deployment requires version tag'
      when:
        - environment == 'production'
        - app_version == 'latest'

    - name: Changed when condition
      command: /usr/local/bin/check_status.sh
      register: result
      changed_when: "'updated' in result.stdout"
      failed_when: result.rc not in [0, 2]

Ansible Vault

# Create encrypted file
ansible-vault create secrets.yml

# Edit encrypted file
ansible-vault edit secrets.yml

# Encrypt existing file
ansible-vault encrypt vars/production.yml

# Decrypt file
ansible-vault decrypt vars/production.yml

# View encrypted file
ansible-vault view secrets.yml

# Rekey (change password)
ansible-vault rekey secrets.yml

# secrets.yml - what `ansible-vault view secrets.yml` shows you.
# On disk this file is ciphertext; it is only ever plaintext in memory and in
# your editor during `ansible-vault edit`. Never commit the decrypted form.
---
db_password: "{{ lookup('env', 'DB_PASSWORD') }}"
api_key: "{{ lookup('env', 'API_KEY') }}"
ssl_key: "{{ lookup('env', 'SSL_PRIVATE_KEY') }}"


# The same file at rest, after `ansible-vault encrypt`:
#   $ANSIBLE_VAULT;1.1;AES256
#   66386439653236336462626566653063336164663966303231363934653561363964363833313662
#   ...

# Use in playbook
---
- name: Deploy with secrets
  hosts: production
  vars_files:
    - secrets.yml
  tasks:
    - name: Configure database
      template:
        src: db.conf.j2
        dest: /etc/db.conf
      no_log: yes # Don't log sensitive data

# Run playbook with vault password
ansible-playbook playbook.yml --ask-vault-pass

# Use password file
ansible-playbook playbook.yml --vault-password-file ~/.vault_pass

# Use multiple vault IDs
ansible-playbook playbook.yml --vault-id prod@prompt --vault-id dev@~/.vault_dev

Testing

Molecule (Role Testing)