What Is a Multiple-machine (Distributed) Configuration


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Introducing the BEA Tuxedo System

A distributed-domain (or multiple-machine) configuration consists of one or more business applications running on multiple machines. Although it includes multiple machines, this type of configuration is considered a single domain because it is administered centrally as a single entity. In other words, all the elements (services, servers, machines, and so on) of all the applications on all the machines in this configuration are defined in, and controlled from, one BEA Tuxedo configuration file.

As a business grows, application developers may need to organize different segments of the business by sets of functionality that require administrative autonomy but allow sharing of services and data. Each functionality set defines an application that may span one or more machines, and that is administered independently from other applications. Such a functionally distinct application is referred to as a domain.

The names of domains frequently reflect the functionality provided. When domains have names such as "marketing" and "research and development," it is easy for customers to find the applications they need.

The basic parts of a configuration distributed across multiple machines are illustrated in the following diagram.

Distributed Application

Parts of a Distributed Configuration

Multiple Machine Part
Description

BRIDGES

BEA Tuxedo system-supplied servers within a domain that send and receive service requests between machines, and route requests to local servers (literally, to local server queues).

Bulletin Board (BB)

A shared memory segment that holds configuration and dynamic information for the system. It is available to all BEA Tuxedo processes.

Bulletin Board Liaison (BBL)

A BEA Tuxedo administrative process that monitors both the data stored in the bulletin board (including any changes made to it), and all application programs.

Clients

Executable programs that periodically request services through the BEA Tuxedo system. (Client programs are usually by customers.)

Distinguished Bulletin Board Liaison (DBBL)

A process dedicated to making sure that the BBL server on each machine is alive and functioning correctly. This server runs on the Master machine of a domain and communicates directly with all administration facilities.

Message queues

Communication between clients and servers is performed through operating-system supported, memory-based message queues.

Messaging paradigms

Different models of transferring messages between a client and a server. Examples include request/response mode, conversational mode, events, and unsolicited communication.

Servers

Executable programs that offer named services through the BEA Tuxedo system. (Server programs are normally written by customers.)

Workstation Handler (WSH)

A multi-contexted gateway process on a server that manages service requests from Workstation clients (that is, client processes running on remote sites).

Workstation Listener (WSL)

A server process running on an application site that listens for and distributes connections from Workstation clients (client processes running on remote sites).

ULOG (User Log)

A file in which error messages are stored.

Multiple Machine Part	Description
BRIDGES	BEA Tuxedo system-supplied servers within a domain that send and receive service requests between machines, and route requests to local servers (literally, to local server queues).
Bulletin Board (BB)	A shared memory segment that holds configuration and dynamic information for the system. It is available to all BEA Tuxedo processes.
Bulletin Board Liaison (BBL)	A BEA Tuxedo administrative process that monitors both the data stored in the bulletin board (including any changes made to it), and all application programs.
Clients	Executable programs that periodically request services through the BEA Tuxedo system. (Client programs are usually by customers.)
Distinguished Bulletin Board Liaison (DBBL)	A process dedicated to making sure that the BBL server on each machine is alive and functioning correctly. This server runs on the Master machine of a domain and communicates directly with all administration facilities.
Message queues	Communication between clients and servers is performed through operating-system supported, memory-based message queues.
Messaging paradigms	Different models of transferring messages between a client and a server. Examples include request/response mode, conversational mode, events, and unsolicited communication.
Servers	Executable programs that offer named services through the BEA Tuxedo system. (Server programs are normally written by customers.)
Workstation Handler (WSH)	A multi-contexted gateway process on a server that manages service requests from Workstation clients (that is, client processes running on remote sites).
Workstation Listener (WSL)	A server process running on an application site that listens for and distributes connections from Workstation clients (client processes running on remote sites).
ULOG (User Log)	A file in which error messages are stored.

A configuration that runs on more than one machine requires platform interoperability and server transparency.

Platform interoperability means that your application can rely on intermachine communications even when different machines are running different operating systems, without code customization.
Server transparency means that a client can access a server without specifying its location. The locations of servers are recorded in the bulletin board and accessed as needed. As a result, servers can be moved, dropped, or added to an application dynamically, without needing to change the application itself.

The DBBL and BRIDGE servers support these requirements of a distributed-domain configuration.