Master Ansible: From Installation to Advanced Playbooks and Roles

1. Basic Deployment

Install Ansible

# yum -y install epel-release
# yum list all *ansible*
# yum info ansible
# yum -y install ansible

Ansible configuration files

/etc/ansible/ansible.cfg    Main configuration file
/etc/ansible/hosts          Inventory
/usr/bin/ansible-doc        Help files
/usr/bin/ansible-playbook   Playbook runner

Define Inventory

# cd /etc/ansible/
# cp hosts{,.bak}
# > hosts
# cat hosts
[webserver]
127.0.0.1
192.168.10.149

[dbserver]
192.168.10.113

Key‑based SSH connection

# ssh-keygen -t rsa
# ssh-copy-id -i /root/.ssh/id_rsa.pub [email protected]
# ssh-copy-id -i /root/.ssh/id_rsa.pub [email protected]
# ssh-copy-id -i /root/.ssh/id_rsa.pub [email protected]

Help commands

# ansible-doc -l               List all modules
# ansible-doc -s MODULE_NAME   Show details of a module

Ansible command basics

ansible <host-pattern> [-f forks] [-m module_name] [-a args]

# Example:
ansible 192.168.10.113 -m command -a 'date'
ansible webserver -m command -a 'date'
ansible all -m command -a 'date'

2. Common Modules

command   # Execute a command (default module)
cron      # Manage cron jobs
user       # Manage user accounts
group      # Manage groups
copy       # Copy files to remote hosts
file       # Manage file attributes
ping       # Test connectivity
service    # Manage service state
shell       # Run complex commands with pipes, variables, etc.
script       # Copy and execute a local script
yum          # Install/remove packages
setup        # Gather facts about remote hosts

3. Ansible Playbook Structure

inventory      # Target hosts
modules        # Modules to invoke
ad hoc commands# Commands to run on hosts
playbooks      # Collection of plays
  tasks        # List of tasks (module calls)
  vars         # Variables
  templates    # Jinja2 templates
  handlers     # Event‑driven actions
  roles        # Reusable components

4. YAML

4.1 Introduction

YAML is a human‑readable data‑serialization format. It emphasizes readability, supports comments, and can represent scalars, lists, and mappings.

4.2 Syntax

name: john smith
age: 41
gender: male
spouse:
  name: jane smith
  age: 37
  gender: female
children:
  - name: jimmy smith
    age: 17
    gender: male
  - name: jenny smith
    age: 13
    gender: female

5. Core Ansible Elements

5.1 Variables

Variable names may contain letters, numbers, and underscores, and must start with a letter.

5.1.2 Facts

Facts are automatically gathered system information. Retrieve them with:

# ansible hostname -m setup

5.1.3 Register

Capture a task’s output into a variable for later use:

tasks:
  - shell: /usr/bin/foo
    register: foo_result
    ignore_errors: True

5.1.4 Pass variables on the command line

# ansible-playbook test.yml --extra-vars "hosts=www user=mageedu"

5.1.5 Pass variables via roles

- hosts: webserver
  roles:
    - common
    - { role: foo_app_instance, dir: '/web/htdocs/a.com', port: 8080 }

5.2 Inventory

Group hosts in /etc/ansible/hosts using INI‑style sections. Example:

ntp.magedu.com

[webserver]
www1.magedu.com:2222
www2.magedu.com

[dbserver]
db1.magedu.com
db2.magedu.com
db3.magedu.com

Host‑specific variables can be added directly:

[webserver]
www1.magedu.com http_port=80 maxRequestsPerChild=808
www2.magedu.com http_port=8080 maxRequestsPerChild=909

Group variables are defined in a [group:vars] section:

[webserver:vars]
ntp_server=ntp.magedu.com
nfs_server=nfs.magedu.com

5.3 Conditional Tests

Use when to run a task only if a condition is true:

- name: Shutdown Debian systems
  command: /sbin/shutdown -h now
  when: ansible_os_family == "Debian"

5.4 Loops

Repeat a task with with_items (or newer loop syntax):

- name: Add server users
  user: name={{ item }} state=present groups=wheel
  with_items:
    - testuser1
    - testuser2

6. Handlers

Handlers run only when notified by a task that reports a change:

- name: Install configuration file
  copy: src=conf/httpd.conf dest=/etc/httpd/conf/httpd.conf
  notify:
    - restart httpd

handlers:
  - name: restart httpd
    service: name=httpd state=restarted

7. Roles

Roles provide a structured way to reuse playbook components. A typical role layout:

roles/
  webserver/
    tasks/main.yml
    handlers/main.yml
    files/…
    templates/…
    vars/main.yml
    meta/main.yml

Include a role in a playbook:

- hosts: webserver
  roles:
    - common
    - webserver

Pass parameters to a role:

- hosts: webserver
  roles:
    - { role: foo_app_instance, dir: '/opt/a', port: 5000 }
    - { role: foo_app_instance, dir: '/opt/b', port: 5001 }

8. Tags

Tags let you run or skip specific parts of a playbook:

- name: Install configuration file
  template: src=conf/httpd.conf.j2 dest=/etc/httpd/conf/httpd.conf
  tags:
    - conf
  notify:
    - restart httpd

# Run only tasks tagged "conf"
ansible-playbook site.yml --tags conf

Author: kangvcar – Source: https://my.oschina.net/kangvcar/blog/1830155