IIS Application Pool - don't mix your framework

In IIS, we can convert each virtual folder into an Application Folder. We can then configure the Application to run a specific version of the .Net Framework.

When IIS 6 was introduced with Windows 2003, Application Pools were also introduced to improved the stability of IIS. You can then group applications into an Application pool. So you can dedicate application pool for critical application or group them accordingly.

This week, I found there is one thing that should be considered when grouping these applications. Make sure that all the applications grouped under the same application pool is running on the same Framework version. I found out the hardware, when we upgraded one of the application to Framework 2.0 which support multilingual feature in asp.net.

However, after that we found that we kept hitting error "Application Not Available" and had to restart the application pool to get the application back. It happens intermittently between the Framework 2.0 application and the Framework 1.1 application.

I suspect it is caused by the cache in the worker process.