How are modules defined and used in Ansible for task automation?

In Ansible, modules are separate scripts or programs that perform specific tasks on managed hosts, such as copying files, installing packages, managing services, etc. Modules allow abstraction of implementation details and provide idempotency — re-running a module will not change the state if it already matches the desired state.

Modules are used in playbooks through tasks. A task specifies the module name and parameters for it. For example:

- name: Install nginx
  apt:
    name: nginx
    state: present

Here, apt is a module for managing packages on Debian/Ubuntu-based systems.

Modules can be built-in (core), third-party, or custom. Ansible automatically copies the module to the target host and executes it there.

Thus, modules in Ansible are building blocks of automation that allow declarative operation descriptions and enable efficient and reliable system configuration management.