Ansible is a automation and provisioning tool that makes it easy to configure systems with the needed software, configuration options and even content. It is a command line tool, written in Python, that uses SSH connections to run these actions. This means that all you need to do is have a viable SSH connection to a machine and Ansible will run any actions you want to run. Ansible can either run single commands or use what is called a playbook to run several commands. Ansible playbooks are written in YAML, which makes understanding them quite easy.
Many systems and applications require certain access to certain ports and protocols. When installing these systems using Ansible it is necessary to also open up the needed ports so that the systems can function correctly. As there is no iptables module in Ansible the shell command is needed to add the iptables rules.
As an example, here is a task that adds a iptables rule to allow Apache to communicate on port 80.
It is best practice to use Ansible with SSH keys in order to create the SSH connections to the servers. This does require a little bit of extra setup before hand in order to ensure that the server can be reached by Ansible via SSH keys alone. As I have been doing this quite a lot recently I decided to package the setup steps into an Ansible playbook.