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Determining Web Site Compatibility with Worker Process Isolation Mode

Updated: August 22, 2005

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

IIS 6.0 can run in one of two distinct modes of operation, which are called application isolation modes. Application isolation is the separation of applications by process boundaries that prevent the applications from affecting one another, and is configured differently for each of the two IIS isolation modes: IIS 5.0 isolation mode and worker process isolation mode.

Worker process isolation mode takes advantage of the redesigned architecture for IIS 6.0. This isolation mode runs all application code in an isolated environment; however, unlike earlier versions of IIS, IIS 6.0 provides isolation without a performance penalty because there are no added process hops. Worker process isolation mode is compatible with most existing Web sites and applications. Whenever possible, run IIS 6.0 in worker process isolation mode to take advantage of the enhanced performance and security in IIS 6.0. When IIS 6.0 is configured to use worker process isolation mode, the metabase property IIs5IsolationModeEnabled contains a value of False.

IIS 5.0 isolation mode provides compatibility for applications that depend upon the process behavior and memory model of IIS 5.0. Run IIS in this mode only when a Web site or application has compatibility issues when running in worker process isolation mode and you cannot resolve the problem. When IIS 6.0 is configured to use IIS 5.0 isolation mode, the metabase property IIs5IsolationModeEnabled contains a value of True.

ImportantImportant
IIS 6.0 cannot run both application isolation modes simultaneously on the same server. Therefore, on a single server running IIS 6.0, you cannot run some Web applications in worker process isolation mode and others in IIS 5.0 isolation mode. If you have applications that require separate modes, you must run them on separate servers.

After you install the target server, IIS is configured to use worker process isolation mode by default. The only reason for configuring IIS to use IIS 5.0 isolation mode is if there are Apache extensions that run only in IIS 5.0 isolation mode. For example, if the preprocessor for the dynamic content in an Apache Web site is incompatible with worker process isolation mode, you must configure IIS to use IIS 5.0 isolation mode. Determine Web site compatibility, in particular Apache-specific extensions to the Web sites, with IIS in your lab before migrating your existing Apache Web sites. In most cases, IIS hosts the Web sites in worker process isolation mode without any problems.

For more information about how to migrate Apache-specific extensions and how to determine compatibility of these extensions with worker process isolation mode, see Migrating Apache-Specific Extensions.

noteNote
Identifying a complete list of potential incompatibilities that Web sites can experience with worker process isolation mode is beyond the scope of the content in this section. Even after following the guidelines in this section, you need to verify in your lab whether your Web sites are compatible with worker process isolation mode.

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