Building Distributed
Applications
Using the Progress AppServer


Application Services

An Application Service is the entire business function provided by an AppServer. An Application Service name is essentially an arbitrary alias for the AppServer that provides that specific function. An AppServer instance can register with more than one Application Service name to identify its function. Because the different Application Service names registered by an AppServer are simple aliases, a client application can call any remote procedure supported by the AppServer instance no matter what Application Service name the client uses to connect the AppServer.

For example, an AppServer instance that accesses an inventory database with certain 4GL procedures might support an Application Service named "Inventory". An AppServer instance that accesses an employees database with certain other 4GL procedures might support an Application Service named "Employees". On the other hand, the same AppServer instance might support both the "Inventory" and "Employees" Application Services.

Assigning Application Service Names

You specify the Application Service names that an AppServer supports when you configure an AppServer instance. Client applications use the Application Service names you specify to indicate an AppServer instance with which to connect. The NameServer then chooses a particular AppServer instance to connect based on whether it supports the Application Service specified by the client.

Fault-tolerant AppServer Support

When distributing connection requests for fault-tolerant AppServers, the controlling NameServer assumes that all AppServer instances that support the same Application Service also support the same API. The NameServer does not validate this assumption. You must ensure that the same published API is available on all AppServer instances that register the same Application Service name with a NameServer. For more information on fault-tolerant AppServers, see the "Fault-tolerant AppServers and Load Balancing" section.

Default Service

A client application can connect to an AppServer without specifying an Application Service. In this case, the NameServer uses whatever AppServer registers itself as the default service. You can specify any AppServer instance as the default service during AppServer configuration. However, Progress Software Corporation recommends that you avoid relying on the default service and provide explicit Application Service names for access by all client applications. For more information on AppServer configuration, see Administration."


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