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Jerry Hewett
Asked: 2011-01-08 13:19:45 +0800 CST

IIS 7.5, Multiple Application Pools, and URL Rewriting (403.18 -- Forbidden)

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Is there any way to configure IIS 7.5 to perform URL rewrites to different application pools on the same site without running into a 403.18 error?

We're using Helicon ISAPI Rewrite 3 on IIS 6 and it's working like a charm. The root-level "application" is running under it's own application pool, and on IIS 6 we have no problems doing URL rewrites from that application pool to any one of the other four application pools. But when I copy the same server configuration information over to IIS 7.5 the URL rewrites to any of the other application pools fail with a "403.18 -- Forbidden" error.

The weird bit is that the IIS 6 is not (at least as far as I can tell, by looking at the site Service configuration dialog) running under IIS 5 emulation mode, so somehow the rewrites aren't throwing 403.18 errors. So something must be different... but whatever it is, I sure haven't been able to figure it out.

Btw, we're not married to Helicon ISAPI Rewrite. If there's another way to preserve our current rewrite configuration rules using another module or method I'd be more than happy to use it.

iis-7.5 application-pools isapi-rewrite

5 Answers

  1. In IIS you cannot just route request from one application to another. Applications are isolated, that is why you are getting 403 error.

    You can proxy requests using either ISAPI_Rewrite, Ape or ARR - it does not matter because request will be passed to another application using local HTTP request anyway. This solution is quite stable, but you will lose some performance.

    Redirect is probably not an option here, because it will generate two request to the server anyway, but since request will be generated by the user with slow connection performance may drop significantly.

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  2. It's not supported in IIS7 for Microsoft's new URL Rewrite component either. The same issue occurs.

    I didn't remember that it was possible in IIS6 to rewrite across app pools. You're doing a rewrite and not a redirect? A redirect will work in IIS7.

    I would ask Helicon at www.isapirewrite.com. They are good responding on their forums. Possibly ISAPI modules live fully within the w3wp.exe process now and thus can't hand off their request to another app pool.

    The other place to ask the question would be at http://forums.iis.net/. The IIS dev team respond to some of the posts and they may provide details on why even ISAPI Rewrite's functionality changed when moving to IIS7.

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  3. Indeed this is not possible with URL Rewrite, however if you really want to do it, you could use ARR (Application Request Routing) in conjunction and it will work, however do note that it would be really doing a complete new request for it, in other words it will work as a proxy issuing a new HTTP Request to itself, for that you need to rewrite to use the full URL including Host name and all. This is a big overhead so only if critical for the application.

    Of course as already mention by Scott Forsyth, the other option is to use a Redirect.

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  4. We also used to use ISAPI Rewrite 3 on IIS6, but when we moved to IIS7.5 we switched over to Helicon APE and it has worked even better then Rewrite. You can use the data in your db to rewrite the urls.

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  5. This is the closet thing I have found that comes close to mod_rewrite for IIS.

    http://www.iis.net/download/URLRewrite

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