If you like me are just trying out ansible and do not want to make a inventory file, because you are just trying it against a single host, but you keep seeing this annoying message:
ERROR: Unable to find an inventory file, specify one with -i ?
You have likely ended up with making a inventory file, but you can actually run ansible against a single host.
Running only on a single host
ansible-playbook webserver.yml -i 10.10.10.10,
Noticed the following comma? That is because if ansible notices a comma, it thinks it is a list of hosts, but you are actually only defining one.
Annoying but reality.