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¶

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

Listing 87. Inventory file¶

[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.

Listing 88. Ansible tasks¶

- name: install httpd
  package: name=apache2 state=latest

2.7. Roles¶

Specialized list of commands to perform

Listing 89. Ansible tasks¶

- name: install httpd
  package: name=apache2 state=latest

- name: write apache config file
  template: src=conf/httpd.j2 dest=/etc/httpd.conf

- name: start httpd
  service: name=httpd state=running

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.

Listing 90. Ansible Playbook¶

- name: install and start apache
  hosts: webservers
  remote_user: myuser
  become_method: sudo
  become_user: root

  vars:
    http_port: 80
    max_clients: 200

  tasks:
  - name: install httpd
    apt: name=apache2 state=latest
  - name: write apache config file
    template: src=conf/httpd.j2 dest=/etc/httpd.conf
  - name: start httpd
    service: name=httpd state=running

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

2.9. Templates¶

Jinja2 templates (similar to Django templates)

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