Oracle Application Server 10g Architecture and Administration - Hardware Architecture of Application Server 10g
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Figure 1-4 shows that you can have multiple instances of the components at each tier. In this example, you see two sets of Oracle HTTP Servers (OHS), each listening on a different port for incoming database requests. As requests enter the system, OHS passes them to the least-loaded Application Server 10g instance on the app server tier.
At the app server tier, there may be multiple instances of Application Server 10g and multiple instances of the Oracle Forms Server, Oracle Developer, and Oracle Reports. These multiple instances are normally on separate servers, and this provides administrators with the ability to create an infinitely scalable architecture. Whenever any components at any tier become overwhelmed, administrators can create a new instance on a new server, add the instance into the Application Server 10g architecture using Oracle Universal Installer, and maintain it using the Enterprise Manager.
The Application Server 10g instances will connect to the database tier. For very large systems, Real Application Clusters (RAC) provides the ability to have multiple instances of the database, all mapping to a single database. Using the same technique as the other tiers, whenever the existing instances become overloaded, another Application Server 10g instance can be created on a new server, and the server can be added to the architecture.
This ability to scale by adding new instances and servers is a critical aspect of Application Server 10g administration because it is the single most important tool for ensuring that the system always has adequate hardware resources.
Functional Architecture of Application Server 10g
Now let’s look at the same architecture from a functional perspective. Figure 1-5 shows the functions of the instances at each level, and this should give you an idea about how the multitiered architecture is used to isolate the logical components of the application.
At the web tier, the main functions are the listener, which listens on a specific port for incoming requests; Web Cache components, which store web page components; and the load-balancing mechanism for ensuring optimal allocation of computing resources to the app server tier. The web tier is managed by the Oracle HTTP Server, which is based on the Apache web server.
The app server tier controls all of the business logic and content assembly. Components such as Oracle Portal are used to define web page components, Oracle Reports defines content specifications, and Oracle Single Sign-On (SSO) controls security for the app server layer. At the database tier are the standard Oracle data management functions for the storage and retrieval of application data. All the components running on the application tier can connect to and retrieve data from the database using any of the available J2EE database connection methods. These are discussed in detail in later chapters. However, Application Server 10g may have its own database if you install the Application Server 10g Infrastructure. With Infrastructure, an Oracle Database instance called iasdb manages Application Server 10gcomponents and security, and preserves its usage data.
Now that you understand the Application Server 10g architecture from a high level, let’s take a closer look at each of these tiers and see how they interact with each other.
 This chapter is from Oracle Application Server 10g Administration Handbook, by Garmany and Burleson. (McGraw-Hill/Osborne, 2004, ISBN: 0072229586). Check it out at your favorite bookstore today. Buy this book now.
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