Backend TypesWe begin our discussion on the three primary types of backend classifications. By backend we meanwhere the message goes after DataPower has processed it—is the destination known in advance orwill it be determined dynamically at runtime? Or perhaps there is none—the appliance returns theresponse directly to the client. A service can use one of three types of backend destinations:• Static Backend—Statically determined by the configuration of the service• Dynamic Backend—Dynamically determined during runtime• Loopback—None at all, in which case the device returns a response to the client withouta backend destination

Static BackendsAs the name implies, Static Backends are those whose attributes are known in advance. At configurationtime, when you are creating the service on the DataPower appliance, you can simply providethe hostname, port, or other information about the backend server required by your service. In some cases, particularly for stateless operations such as Web services, you might want tosend messages to a group of backend servers to distribute load and facilitate high availability.This is sometimes referred to as spraying or load balancing messages. DataPower has somecapability to act as a load balancer. In this case, you provide the name of a load-balancer objectconfiguration that you have created for the backend address, rather than a single hostname.

Dynamic Backends

LoopbackIn some cases, there might not be a backend, particularly given the broad spectrum of use casesfor message processing that can be accomplished using the DataPower appliances directly. Wediscuss the many available processing actions that can be applied to request and response ruleslater in this chapter, and you can see many of them in use throughout the book.Another typical use for the loopback configuration is simple testing or development whenthe backends are not available and when creating utility services on the appliance that are meantsolely to provide some capability to other services on a localhost interface.Of course, when choosing the loopback backend configuration, the server address and portfields will also not appear on the service configuration page.