While using Ansible 2.4.3 for the very first time after upgrading, I received the following error:
[DEPRECATION WARNING]: [defaults]hostfile option, The key is misleading as it can also be a list of hosts, a directory or a list of paths . This feature will be removed in version 2.8.
It looks like if you have hostfile = ./hosts within the ansible.cfg file, you would have to change it to inventory = ./hosts