Evaluating Application Requirements

Applies To: Windows Server 2003, Windows Server 2003 with SP1

IIS 6.0 cannot run both application isolation modes simultaneously on the same computer. Therefore, on a single computer running IIS 6.0, you cannot run some Web applications in worker process isolation mode and others in IIS 5.0 isolation mode. Applications that require different application isolation modes must be run on separate computers.

Guidelines for Optimizing Application Performance

When you are deciding which application isolation mode to use, follow these guidelines:

• Use worker process isolation mode unless you need to use IIS 5.0 isolation mode because of a specific compatibility issue. For example, read raw data filters only work in IIS 5.0 isolation mode.

• Run Web sites that contain static content or simple ASP applications in worker process isolation mode. These Web sites usually require little or no modification to run in worker process isolation mode.

• For applications that run correctly in IIS 5.0, try running them first in worker process isolation mode. If they do not work correctly, attempt to diagnose and resolve any compatibility issues. You can also turn off or scale down some of the features that worker process isolation mode provides. For example, you might turn off recycling or change the recycling settings so that the server does not perform an overlapped recycle.

If a server is running in IIS 5.0 isolation mode and you upgrade the servers applications so that they are compatible with worker process isolation mode, be sure to change the isolation mode on that server to worker process isolation mode. If, after changing the server from IIS 5.0 isolation mode to worker process isolation mode, you find that you cannot easily maintain a healthy server, change back to IIS 5.0 isolation mode while you diagnose and fix the compatibility issues. Then reconfigure the server to run in worker process isolation mode.

Applications That Cannot Run in Worker Process Isolation Mode

Applications that run in worker process isolation mode can take advantage of all the worker process behaviors, which include multi-instancing, recycling, and configurable process identity. Certain application characteristics conflict with the architecture of worker process isolation mode. Applications with those characteristics must be run in IIS 5.0 isolation mode until you can modify them.

Applications with the following characteristics cannot run in worker process isolation mode:

• Read raw data filters. This type of ISAPI filter only works in IIS 5.0 isolation mode.

• Dependency on Inetinfo.exe. Applications that must run within an Inetinfo.exe worker process can only run in IIS 5.0 isolation mode.

• Requires Dllhost.exe. ISAPI applications that must run in a Dllhost.exe environment can only run in IIS 5.0 isolation mode because Dllhost.exe is not available for ISAPI applications in worker process isolation mode. (Dllhost.exe can still be used to host out-of-process COM+ applications, regardless of the mode in which IIS is running.)

If IIS 6.0 is running in worker process isolation mode (the default mode in IIS 6.0), and you must run applications that require a functionality that is only available in IIS 5.0 isolation mode, reconfigure the server to run in IIS 5.0 isolation mode until you can correct the incompatibility. Running your server in IIS 5.0 isolation mode means that you cannot take advantage of the reliability features in worker process isolation mode.