Hosts And Users:

For each play in a playbook, you get to choose which machines in your infrastructure to target and which remote user to complete the tasks. To include hosts in Ansible inventory, we will be using the IP addresses of the host machines.

Generally the hosts are a list one or more groups or host patterns, separated by colons. The remote user is just the name of the user account.

Variables:

Ansible uses variables which are defined previously to enable more flexibility in playbooks and roles. They can be used to loop through a set of given values, access various information like the host name of a system and replace certain strings in templates with specific values.

Ansible already defines a rich set of variables, individual for each system. Whenever Ansible will run on a system, all facts and information about the system are gathered and set as variables.

But there is a rule for naming variables. Variable names should be letters, numbers, and underscores. Variables should always start with a letter. E.g. wamp_21, port5 is valid variable names, whereas 01_port, _server are invalid.

Tasks:

Tasks allow you to break up bits of configuration policy into smaller files. Task includes pull from other files. Tasks in Ansible go with pretty much the English meaning of it.

E.g: Install <package_name>, update <software_name> etc.

Handlers:

Handlers are just like regular tasks in an Ansible playbook, but are only run if the Task contains a notify directive and also indicates that it changed something. For example, if a config file is changed, then the task referencing the config file may notify a service restart handler.

let me give you an example of a playbook which will start the Apache httpd server program:

---
- hosts: webservers
  vars:
    http_port: 80
    max_clients: 200
  remote_user: root
  tasks:
  - name: ensure apache is at the latest version
    yum: name=httpd state=latest
  - name: write the apache config file
    template: src=/srv/httpd.j2 dest=/etc/httpd.conf
    notify:
    - restart apache
  - name: ensure apache is running (and enable it at boot)
    service: name=httpd state=started enabled=yes
  handlers:
    - name: restart apache
      service: name=httpd state=restarted