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On the z/OS and OS/390 platform, the multi-tier J2EE architectures can be translated to two-tier, three-tier, or n-tier logical environments. We discuss the two-tier and three-tier architectures in this book.
This is a simple architecture, where all the tiers except the client tier reside on the same server. It is relatively easy to configure and support and is shown in Figure 1-2 on page 6.
Figure 1-2: Two-tier logical architecture
For this redbook project, our test environment was set up as a two-tier architecture, with the WebSphere Application Server, WebSphere Portal Server, database server, and an LDAP server all installed on the server tier. A Web browser, the Authortime component of WebSphere Portal Content Publishing, and WebSphere Studio Application Developer was installed on a distributed platform, in this case two computers running Windows 2000.
Implementing a three-tier architecture provides several options for a logical view of the architecture. The first option is to put the Web tier components (portlets, JSPs, and servlets) and EJB components on the same server as a middle tier, and the EIS components such as database and applications placed on a third or backend-tier. This is shown in Figure 1-3.
Figure 1-3: Three-tier logical architecture- Option one
Another option would be to keep the Web tier components (portlets, JSPs, and servlets) in the middle tier and co-locate the EJB components along with the EIS components (database and applications) on the back-end server. This option separates the business logic and data access from the presentation layer represented by portal server. This solution is sometimes referred to as the Distributed Application Model. On the zSeries platform, the middle tier and back-end tier could both reside on the same physical hardware, but still be completely separated as logical partitions or LPARs. Figure 1-4 shows option two in a three-tier architecture.
Figure 1-4: Three-tier logical architecture- Option two
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