Os-apply-config apply configuration out of the cloud metadata (JSON) that it receives from a metadata server.

It turns metadata from one or more JSON files like this:

{"keystone": {"database": {"host": "127.0.0.1", "user": "keystone", "password": "foobar"} } }

into service config files like this:

[sql] connection = mysql://keystone:foobar@127.0.0.1/keystone