ASP.NET websites referencing common, updatable Assembly

Question

Hi all,

I'm developing a component (HttpModule) that's used by a number of web applications on a .NET website, and I want the component to be easily maintainable. I've come up with something outlined below but wanted to see if there were any positive/negative thoughts or general feedback on the implementation, as I'm not 100% familiar with Assembly loading, especially in terms of memory overhead.

(I don't really want to do this: http://stackoverflow.com/questions/716483/create-your-own-net-assembly-cache)

The lightweight HttpModule itself is in the GAC and referenced from the site's root web.config. On each request it opens a text file (stored in the web's root/bin) that contains just a strong named's assembly name (e.g. "My.MyLibrary, Version=1.1.0.0, Culture=en, PublicKeyToken=03689116d3a4ae33") and then checks the current AppDomain to see if it is already referenced (iterates over GetAssemblies()). If not, it then calls Assembly.Load to load myLibrary and uses basic Reflection to Invoke() a custom method in My.MyLibrary that actually does the intended processing work of the HttpModule.

My.MyLibrary itself is also in the GAC. To upgrade the app without any app restarts, put a new version in the GAC, and just edit the string in the text file. I'm using the text file because a) it's fast and b) I didn't want to have to update a machine/web.config and cause a recycle to redirect the HttpModule to use a new version of My.MyLibrary. It seems to work okay. The old version can be uninstalled from the GAC when it's finally ready to be. So hopefully the only time an app pool/iis reset would be needed would be to change the HttpModule part.

Any replies much appreciated!

-Will

Answer 1

Personally I would say if you can avoid using any late binding it would be better, but as you want to be able to have the freedom to just throw a new assembly at your application then it does seem like late binding makes sense.

With regards to your method of storing and retrieving the list of assemblies, I would use an XML object and load it from the file. You will find adding extra information to it simpler this way, otherwise you will have to maintain your own file format.

You may also want to consider adding some code to catch errors generated from these assemblies, unload them and put a flag in your file telling your HttpModule not to load it until it has been updated.