The only important tool that is required to be installed and running on the client machine is the OpenSSH-server. All new releases of Linux use SSH as the main remote access method by default.
To make sure that everything is in place, the SSH service should always be running and the system's firewall should allow a port for SSH to service through. By default, this is port 22. This can be changed, however, and this change should be also noted in the host Ansible inventory.
For Linux clients, any extra configuration for Ansible management is more aimed at following best practice guidelines than being strictly necessary. Extra configuration can be a way to make sure that the remote clients managed by Ansible are fully automated, securely accessible, and do not require an admin intervention when running automated tasks.
