Explain how the playbook file structure in Ansible is organized and how it is used for task automation.

A playbook in Ansible is a YAML file that describes a set of tasks for automating configuration and managing infrastructure.

The structure of a playbook typically includes:

• hosts: defines on which hosts the tasks will be executed.
• vars: variables used in the playbook.
• tasks: a list of tasks to perform, such as installing packages, copying files, running commands.
• handlers: special tasks that are triggered upon changes (e.g., restarting a service).
• roles: logical grouping of tasks and configurations for reuse.

Example of a simple playbook:

- hosts: webservers
  vars:
    http_port: 80
  tasks:
    - name: Install nginx
      apt:
        name: nginx
        state: present
    - name: Start nginx
      service:
        name: nginx
        state: started

A playbook is used for sequential and repeatable execution of tasks on remote servers, which simplifies infrastructure management and reduces the likelihood of errors during manual administration.