While developing three-tier OLTP systems is complex and requires specialized skills,
the benefits are substantial. Systems that use application servers provide higher scalability,
availability, and flexibility than the simpler two-tier systems. Determining
which architecture is appropriate for an OLTP system requires (among other things)
careful evaluation and consideration of costs, available skills, workload profiles, scalability
requirements, and availability requirements.
Figure 9-3 illustrates a three-tier system using an application server.
Application Servers and Web Servers
The middle tier of web-based systems is usually an application server and/or a web
server. These servers provide similar services to the application server previously
described, but are more web-centric, dealing with HTTP, HTML, CGI, and Java.
J2EE and .NET application servers have evolved a great deal in the last decade and
are the clear inheritors of the TP monitor legacy for today??™s N-tier systems. Different
companies have different standards and preferences??”the proprietary nature of .
Pages:
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465