How to use custom private key with ansible?

What is the analog for :

ssh -i my_key.pem [ubuntu@123.123.123.123](mailto:ubuntu@123.123.123.123)

in Ansible?

--private-key=PRIVATE_KEY_FILE

This also can be set on a per host or group basis with ansible_ssh_private_key_file, which can be useful if different pems are needed for different sets of machines.

http://docs.ansible.com/intro_inventory.html#id10

Thanks!