Application specific mapping in FastCGI ISAPI 1.5

IIS team recently released FastCGI ISAPI 1.5 for IIS 5.1 and IIS 6.0. One of the major new features added in this release is per application process pools. Per application process pools allow users to specify a unique FastCGI mapping for a particular web application in fcgiext.ini. Using this functionality administrators can now choose to run a web application with PHP version which can be different from what is used for rest of the PHP applications in the same site or the server. This was always possible in IIS 7.0 and 7.5 by overriding PHP handler in web.config but not on WinXP and Win2K3. Version 1.0 of FastCGI ISAPI only allowed specifying a different process pool at a site level granularity. So if a site has both wordpress and gallery installed, it wasn’t possible to use different PHP versions for running them. With FastCGI 1.5 that is possible now. For providing application specific mappings, we extended site specific mapping feature. Let’s learn application specific mapping by comparing it with site specific mapping.


Site specific mapping
Application specific mapping


Above configuration will make FastCGI module pick PHP_53 mapping for all sites but use PHP_52 mapping for site with id 1234.
FastCGI module will pick PHP_520 mapping for gallery and PHP_530 for wordpress defined under site 1234. All other php applications under site 1234 will be handled using PHP_526 mapping. Remaining sites will use PHP_530 mapping.

Application path’s format for fcgiext.ini is “/LM/W3SVC/<siteId>/ROOT/<appname>”. In this format “/LM” and “/W3SVC” parts are option. “/Root” can be emitted for applications pointing to root of the site.

fcgiconfig.js -add -section:php_530 -extension:php -path:c:\php530\php-cgi.exe -site:1234
fcgiconfig.js -add -section:php_530 -extension:php -path:c:\php530\php-cgi.exe -application:/w3svc/1234/root/wordpress
Picking the right mapping
Among all the formats (including wildcard formats) which are accepted in fcgiext.ini mappings, FastCGI goes through following logic to pick which mapping to use for each request.
·         If mapping for current  application is present, it takes highest priority and is used. E.g. php:/w3svc/1234/root/drupal=ApplicationHandler
·         If wildcard mapping for the current application is present, it is used next. E.g. *:/w3svc/1234/root/drupal=ApplicationHandler
·         If mapping for a particular site is present but application specific mapping is not present, than that is used. E.g. php:1234=SiteHandler
·         If site specific and application specific mapping is not present, FastCGI module look for wildcard mapping for a particular site. E.g. *:1234=SiteHandler
·         If none of the above is present, mapping for the file extension takes priority. E.g. php=ExtensionHandler
·         Wildcard mapping comes last. *=WildcardHandler
If FastCGI doesn’t find a mapping after going through the logic above, an error is returned.
What’s coming next
Now that applications can be configured to run using a particular PHP version on IIS 5.1 and above, our next goal is to support multiple PHP versions side-by-side in WebPI. This would require PHP installer to support side-by-side install which is also something we are looking at. Once PHP installer has the required support, we will list different PHP versions in WebPI and let users install multiple versions of PHP. Additionally users will be able to target a particular PHP version when installing a PHP application using WebPI.
Hope this helps.

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