Building Distributed
Applications
Using the Progress AppServer
Run-time Components and Operation
Figure 2–7 shows the major run-time components that comprise the AppServer architecture and their basic relationships. For more information on the complete architecture of an AppServer installation, including AppServer configuration and management, see Administration."
Figure 2–7: AppServer Run-time Components
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The dotted arrows indicate communications required to establish a connection between client applications and the AppServer. Table 2–1 identifies and describes the components shown in Figure 2–7.
Table 2–1: Progress AppServer Run-time Components Component Description Client Application A process that requests the execution of remote 4GL procedures in the context of an AppServer session.A client application can be:The Progress Interface is the code that allows a client application to access an AppServer. For 4GL clients, this interface is accessed through built-in 4GL statements and functions dedicated to AppServer access. For Java and ActiveX clients, this interface is accessed through a set of objects custom built to access AppServer procedures using the Progress Open Client Toolkit (available separately). Application Server process A process that executes remote procedure requests in the context of a Progress session. Much like a batch 4GL client, almost any 4GL statement that you can execute in an interactive 4GL client you can execute within an Application Server process. An AppServer instance typically contains multiple Application Server processes that start up when you start the AppServer.An Application Server process can also act as a 4GL client of another AppServer instance, by making its own remote procedure calls. Application Broker A process that creates, manages, and allocates Application Server processes for access by client applications. The Application Broker manages client connection requests and dispatches requests to Application Server processes. Exactly how it does this depends on the AppServer operating mode.3 A single Application Broker supports one AppServer instance. NameServer4 A process that directs client connection requests to an AppServer that supports a specified business function. A client indicates which AppServer instance it wants to connect to by specifying an Application Service5 name that identifies the required business function.When an AppServer is started, it registers with a NameServer the Application Services that it supports. The NameServer with which an AppServer registers is the controlling NameServer for that AppServer instance.When a client requests a connection to an Application Service, the NameServer directs the client to the AppServer that has registered the specified Application Service.To provide fault-tolerant access to NameServers, you can configure multiple NameServer instances that contain identical information. Each such NameServer is a replica of the others, thus providing connection-level fault-tolerance.If you have installed the load-balancing option, multiple AppServers can also support the same Application Service, allowing the NameServer to distribute client connections among them, thus providing server-level fault tolerance.6Note that to connect an AppServer, the client only needs to know the host and port of the NameServer and the name of an Application Service. The Progress Interface contacts the specified NameServer on behalf of the client, processes the response, and directs the client to the appropriate AppServer.
- For more information, see the WebSpeed Developer’s Guide.
- For more information, see the Progress Open Client Developer’s Guide.
- For more information, see the "Understanding AppServer Operating Modes" section in this manual.
- The same NameServer process can also coordinate Web client access to WebSpeed Servers and 4GL client access to Progress DataServers. For more information on all NameServer features, see the Progress Installation and Configuration Guide Version 9 for UNIX or the Progress Installation and Configuration Guide Version 9 for Windows.
- For more information on Application Services, see the "Connection Process" section in this manual.
- For the NameServer to provide server-level fault tolerance, you must have the Progress AppServer Load Balancer installed.
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