Can you explain what the 'Serial' module in Ansible means and how it is used to control task execution?

In Ansible, the serial parameter is not a separate module but a parameter in the playbook that controls the number of hosts on which tasks are executed simultaneously.

Using serial allows controlling the parallelism of playbook execution, for example, to update servers in batches, minimizing risks and load.

Example of usage in a playbook:

- hosts: webservers
  serial: 2
  tasks:
    - name: Update packages
      apt:
        upgrade: dist

In this example, tasks will be executed on two hosts simultaneously, then on the next two, and so on until all hosts are processed.

This is useful for phased deployment and risk management during updates or changes in infrastructure.