A service is an application that makes data or operations available to network clients. Often, a service is implemented as a formal Microsoft® Win32®-based service, but this is not required.
Service publication is the act of creating and maintaining data about one or more instances of a given service so that network clients can find and use the service. Publishing a service in Active Directory enables clients and administrators to move from a computer-centric view of the distributed system to a service-centric view.
In the Microsoft® Windows NT® Server 3.51 or later operating system, a distributed system was a group of computers running various services. To access a service, an application required data about which computers offered the service.
In the Microsoft® Windows® 2000 Server, Microsoft® Windows® 2000 Advanced Server, and Microsoft® Windows® 2000 Datacenter Server operating systems, services publish their existence using objects in Active Directory. The objects contain binding information that client applications use to connect to instances of the service. To access a service, a client does not need to know about specific computers: the objects in Active Directory include this information. A client queries Active Directory for an object representing a service (called a connection point object) and uses the binding data from the object to connect to the service.
The following table shows examples of bindings.
|File Service||UNC Name for a share.
|RPC Service||Remote procedure call (RPC) binding: special encoded
information used to connect to the RPC server. RPC bindings
can be converted to and from strings with the RPC APIs.
In a distributed system, the computers are engines, and the interesting entities are the services that are available. From the user perspective, the identity of the computer that provides a particular service is not important. What is important is accessing the service itself.
This is also the case with service management. The administrator of a given DNS zone is not interested in the computers running the DNS service; the administrator wants to administer DNS. There will likely be multiple instances of the DNS service, one of which is authoritative. The computers that support DNS service are not important to the DNS administrator. What is important is how to manage the service as a single distributed resource—not as individual processes running on different computers.