Os-apply-config apply configuration out of the cloud metadata (JSON) that it recieves 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