Extending the IIS Configuration System using COM

Today I was going to post about extending the IIS Configuration, in particular about a feature that not everybody knows that allows you to extend the IIS Configuration System using dynamic code. What this means is that instead of hard-coding the configuration using XML in a .config file, your configuration can be provided by a COM object that implements IAppHostPropertyExtension, IAppHostElementExtension and IAppHostMethodExtension.

Then, just to make sure I was not repeating what somebody else already said I searched for this in live.com (Worth to say, excellent results, first hit is the documentation of the interface, second hit is an excellent article in iis.net).

So instead of repeating what you can already find in those places in IIS.NET I decided to not blog about it in details, but instead mention some of the things that are not specified in these places.

This dynamic configuration is great and offers lots of interesting features since it allows you to expose any random code that can immediately be accessed through all of our configuration API's, including Microsoft.Web.Administration, AHADMIN, etc, giving your end-user a common programming paradigm, in fact this also means that its immediately accessible to the UI API's and even to the new Configuration Editor in the Admin Pack.

Another interesting benefit is that through these API's your code can be called remotely so that it can be scripted to manage the machines remotely without the need to write any serialization or complex remote infrastructure (restrictions might apply).

However, one thing that is also important to mention is that these dynamic configuration extensions are only available for administration tools, meaning you cannot access this extensions from the worker process by default. To clarify, you cannot use the Worker Process configuration instance to invoke these extensions since the worker process specifically disables the ability to call them in its configuration instance. However, if you create your own instance of Microsoft.Web.Administration.ServerManager (which requires you to be running in Full Trust) you will be able. You can also create your own instance of Microsoft.ApplicationHost.AdminManager and you will be able to access them. However in both cases this will only work if your an Administrator in the machine or have read ACL's for ApplicationHost.config file (which by default is only readable by Administrators). This is why methods like Microsoft.Web.Administration.WebConfiigrationManager::GetSection (and CoGetObject for AHADMIN) are provided so you don't run into these issues when developing Web Applications and are still able to read configuration sections for your worker process without requiring administrative privileges (in MWA provided you are either are in Full Trust or the section definition marks it as requirePermission=false).

To understand better some scenarios its worth to mention that In IIS 7.0 we actually use these API's to provide access to runtime information in an easy way and other tasks, for example, to query the state of a Site, to Recycle an Application Pool, to assign an SSL certificate to a binding, to stop a Site, are all provided through this mechanism. If you want to see all the things we do this way just open %windir%\System32\Inetsrv\config\schema\rscaext.xml where all of our Web Server extensions are declared. Our own FTP Server for IIS 7.0 uses the same mechanism for things like querying Sessions, and other cool stuff.

Anyway, feel free to give the IIS.NET article a good read, its quite good.


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