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This section describes three architecture designs. Deciding which architecture to choose can be reduced to identifying the following design objectives:
The next three sections describe three architecture designs.
Designing for Vertical Scalability and PerformanceThe architecture example shown in FIGURE 2-6 provides enhanced security. The Web server can be configured as a reverse proxy by receiving an HTTP request on the ingress network side from a client, then opening another socket connection on the appserver side to send an HTTP request to the Web server running inside the Sun ONE Application Server instance. Alternatively, the Web server instance could instantiate EJB components after performing a lookup on the home interface of a particular EJB component. One advantage of this decoupled architecture is independent scaling. If it turns out that the Web server servlets need to scale horizontally, they can do so independently of the application server logic. Similarly, if the EJB architecture's logic needs to scale or be modified, it can do so independently of the Web tier. Potential disadvantages include increased latency between the Web tier and Application Server tier communications and increased maintenance. Figure 2-6. Decoupled Web Tier and Application Server Tier Vertically ScaledDesigning for Security and Vertical ScalabilityThe example shown in FIGURE 2-7 represents a collapsed architecture that takes advantage of the Web server already included in the Sun ONE Application Server instance process. This architecture is suitable for applications that have relatively intensive servlet-to-EJB communications and less stringent security requirements. From an availability standpoint, fewer horizontal servers result in lower availability. A potential advantage of this architecture is lower maintenance cost because there are fewer servers to manage and configure. Figure 2-7. Tightly Coupled Web Tier and Application Server Tier Vertically ScaledDesigning for Security and Horizontal ScalabilityThe architecture shown in FIGURE 2-8 is a more horizontally scaled variant of the architecture shown in FIGURE 2-6. This results in increased availability. More server failures can be tolerated without bringing down services in this configuration. Figure 2-8. Decoupled Web Tier and Application Server Tier Horizontally Scaled |
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