Dig deeper into Ansible and F5 integration
Yes there is another file called the host file which needs to have information about the host you are trying to connect to.
"Ansible works against multiple systems in your infrastructure at the same time. It does this by selecting portions of systems listed in Ansible’s inventory, which defaults to being saved in the location /etc/ansible/hosts. You can specify a different inventory file using the -i option on the command line." - http://docs.ansible.com/ansible/latest/intro_inventory.html
Example of the host file for the above example:
[bigip]
10.XX.XX.XX
[bigip:vars]
username=admin
password=admin
When the playbook is run it will look at the host file. As mentioned above default host file is placed at /etc/ansible/hosts BUT you can create your own host file as well and then reference that host file in your ansible.cfg.
Example of ansible.cfg
[defaults]
inventory = ./your_host_file