Master Ansible: From Installation to Advanced Playbooks and Roles

1. Basic Setup

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 config file
/etc/ansible/hosts          Inventory
/usr/bin/ansible-doc        Help
/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

Connect using SSH keys

# 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]

Helpful commands

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

Basic Ansible command syntax

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   # default module, runs a command on remote hosts
cron      # schedule jobs (minute, hour, day, month, weekday, state)
user      # manage user accounts (name, uid, groups, home, etc.)
group     # manage groups (name, gid, state)
copy      # copy files to remote hosts (src, dest, owner, mode, content)
file      # manage file attributes and symlinks
ping      # test connectivity
service   # manage service state (enabled, name, state)
shell     # run complex commands with pipes, variables
script    # copy and execute a local script on remote hosts
yum       # install/remove packages
setup     # gather facts from remote hosts

3. Ansible Playbook Structure

A playbook consists of inventory, modules, ad‑hoc commands, and a list of plays. Each play defines hosts, variables, tasks, handlers, and optional roles.

4. YAML

4.1 Introduction

YAML (YAML Ain't Markup Language) is a human‑readable data‑serialization format used for Ansible playbooks and inventory files.

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.

Facts

Facts are gathered from remote hosts and stored as variables. Retrieve all facts with:

# ansible hostname -m setup

Register

Capture task output into a variable for later use:

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

Passing variables via CLI

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

Passing variables through roles

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

5.2 Inventory

Group hosts in INI‑style files. Example:

ntp.devopsman.cn

[webserver]
www1.devopsman.cn:2222
www2.devopsman.cn

[dbserver]
db1.devopsman.cn
db2.devopsman.cn
db3.devopsman.cn

[webserver]
www[01:50].example.com

[databases]
db-[a:f].example.com

Host variables

[webserver]
www1.devopsman.cn http_port=80 maxRequestsPerChild=808
www2.devopsman.cn http_port=8080 maxRequestsPerChild=909

Group variables

[webserver]
www1.devopsman.cn
www2.devopsman.cn

[webserver:vars]
ntp_server=ntp.devopsman.cn
nfs_server=nfs.devopsman.cn

Group nesting

[apache]
httpd1.devopsman.cn
httpd2.devopsman.cn

[nginx]
ngx1.devopsman.cn
ngx2.devopsman.cn

[webserver:children]
apache
nginx

[webserver:vars]
ntp_server=ntp.devopsman.cn

Inventory parameters

ansible_ssh_host
ansible_ssh_port
ansible_ssh_user
ansible_ssh_pass
ansible_sudo_pass
ansible_connection
ansible_ssh_private_key_file
ansible_shell_type
ansible_python_interpreter

5.3 Conditional Tests

Use when statements with Jinja2 expressions to run tasks conditionally.

tasks:
  - name: "shutdown Debian flavored system"
    command: /sbin/shutdown -h now
    when: ansible_os_family == "Debian"

  - command: /bin/false
    register: result
    ignore_errors: True
  - command: /bin/something
    when: result|failed
  - command: /bin/something_else
    when: result|success

5.4 Loops

Iterate over items with with_items (or the newer loop syntax).

- name: add server user
  user:
    name: "{{ item }}"
    state: present
    groups: wheel
  with_items:
    - testuser1
    - testuser2

6. Templates

# Example Jinja2 snippet in a template
MaxClients {{ maxClients }}
Listen {{ httpd_port }}

7. Ansible Playbooks

A playbook is a list of plays. Each play maps hosts to a set of tasks.

- hosts: webserver
  vars:
    http_port: 80
    max_clients: 256
  remote_user: root
  tasks:
    - name: ensure apache is at the latest version
      yum:
        name: httpd
        state: latest
    - name: ensure apache is running
      service:
        name: httpd
        state: started
  handlers:
    - name: restart apache
      service:
        name: httpd
        state: restarted

7.1 Playbook components

Hosts and Users

Define which hosts a play runs on and under which remote user.

Task list and actions

Each task calls a module with parameters; modules are idempotent.

Handlers

Tasks that run only when notified by other tasks.

8. Roles

Roles provide a structured way to organize playbooks, separating files, templates, tasks, handlers, vars, and meta.

# Directory layout example
roles/
  common/
    tasks/main.yml
    handlers/main.yml
    files/…
    templates/…
    vars/main.yml
  webserver/
    tasks/main.yml
    …

# Using roles in a playbook
- hosts: webserver
  roles:
    - common
    - webserver

8.1 Creating a role

Create a roles directory.

Create sub‑directories for each role (e.g., webserver).

Inside each role, create tasks, files, templates, handlers, vars, meta (and optionally defaults).

Reference the role in your playbook.

9. Tags

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

- hosts: webserver
  tasks:
    - name: install httpd package
      yum:
        name: httpd
        state: latest
    - name: configure httpd
      template:
        src: httpd.conf.j2
        dest: /etc/httpd/conf/httpd.conf
      tags: conf
      notify: restart httpd
  handlers:
    - name: restart httpd
      service:
        name: httpd
        state: restarted

Run only tasks with the conf tag: ansible-playbook site.yml --tags conf.