2. Basic Concepts

2.1. Core concepts

Human readable configuration files
Tasks executed in order
Configuration management
Workflow orchestration
App deployment
Agentless architecture (no need to install anything on managed nodes)
Uses OpenSSH
Secure
Playbooks
Make change only when needed (if there was a change)
Changes can be incremental or wholesale
Schedule tasks daily, weekly, or monthly
Perform regular state check and validation
Automate backup and restore

2.2. Control node

Any machine with Ansible installed.
You can run commands and playbooks, invoking /usr/bin/ansible or /usr/bin/ansible-playbook, from any control node.
You can use any computer that has Python installed on it as a control node - laptops, shared desktops, and servers can all run Ansible.
However, you cannot use a Windows machine as a control node.
You can have multiple control nodes.

2.3. Managed nodes

The network devices (and/or servers) you manage with Ansible.
Managed nodes are also sometimes called "hosts".
Ansible is not installed on managed nodes.

2.4. Inventory

Filename: hosts
A list of managed nodes.
An inventory file is also sometimes called a "hostfile".
Your inventory can specify information like IP address for each managed node.
An inventory can also organize managed nodes, creating and nesting groups for easier scaling.
Default inventory file location /etc/ansible/hosts
If any other location, then specify ansible -i hosts ... for file named: hosts
More info

Code 2.11. Inventory file named hosts

[dbservers]
db01.example.com
db02.example.com

[webservers]
10.13.37.1
10.13.37.2
10.13.37.3

2.5. Modules

The units of code Ansible executes.
Each module has a particular use, from administering users on a specific type of database to managing VLAN interfaces on a specific type of network device.
You can invoke a single module with a task, or invoke several different modules in a playbook.

Categories:

Cloud modules

Clustering modules

Commands modules

Crypto modules

Database modules

Files modules

Identity modules

Inventory modules

Messaging modules

Monitoring modules

Net Tools modules

Network modules

Notification modules

Packaging modules

Remote Management modules

Source Control modules

Storage modules

System modules

Utilities modules

Web Infrastructure modules

Windows modules

More info at: https://docs.ansible.com/ansible/latest/modules/modules_by_category.html#modules-by-category

2.6. Tasks

The units of action in Ansible.
You can execute a single task once with an ad-hoc command.

Code 2.12. Ansible tasks

- name: Install
  package: name=nginx state=latest

2.7. Roles

Specialized list of commands to perform

Code 2.13. Ansible tasks

    - name: Install
      package: name=nginx state=latest

    - name: Configuration
      template: src=nginx.conf dest=/etc/nginx/http.d/default.conf

    - name: Setup
      file: path=/var/www state=directory owner=myuser group=www-data mode=755

    - name: Enable
      service: name=nginx enabled=yes

    - name: Start
      command: nginx -c /etc/nginx/nginx.conf

2.8. Playbook

Ordered lists of tasks, saved so you can run those tasks in that order repeatedly.
Playbooks can include variables as well as tasks.
Playbooks are written in YAML and are easy to read, write, share and understand.

Code 2.14. nginx.yaml (ansible playbook)

- name: Install and configure nginx
  hosts: all
  become: yes

  vars:
    http_port: 80

  tasks:
    - name: Install
      package: name=nginx state=latest
    - name: Configuration
      template: src=nginx.conf dest=/etc/nginx/http.d/default.conf
    - name: Setup
      file: path=/var/www state=directory owner=myuser group=www-data mode=755
    - name: Enable
      service: name=nginx enabled=yes
    - name: Start
      command: nginx -c /etc/nginx/nginx.conf

2.9. Templates

Jinja2 templates
Similar to Django templates

<ul>
{% for item in sequence %}
    <li>{{ item }}</li>
{% endfor %}
</ul>