Access of data center resources is provided by the present invention using stateless and stateful Web services. For stateless Web services, the present invention provides an invoker API that allows a client to invoke a specific resource and perform an operation on the resource. For stateful Web services, the present invention provides a Web Service Definition file that defines attributes and operations for data center resources. The client may access an instance of a Web service resource once an endpoint reference is obtained from the server. Since the resource instance is persistent, the client may invoke data center operations and manipulate the resource attributes accordingly.