Drawback to creating a separate IIS application pool for each website / application

Question

Currently, on our production IIS web farm, we host about 15 applications in a single App Pool (Default App Pool). There are two websites and about 13 virtual directories.

Answer 1

I doubt they were built with that requirement in mind unless they rely on shared memory for some reason. Otherwise, for the scenario described...

Pros (of separate app pool):

• process isolation (one crash doesn't bring down the others)
• less resource contention
• more memory available for in-proc sessions, cache

Cons:

• more processes, memory, and context switchces
• shared cache scenarios no longer available*

*I'm not sure how .NET segregates websites in the same app pool as it pertains to the HttpRuntime cache; for Sessions, "application uniqueness" (1) is determined by:

• The physical path on all servers (case sensitive)
• The machine key
• The instance id
• The approot

This is what prevents you from sharing sessions across different websites in the same app pool, for instance; but it might be easier to share cache data though. By and large, the discussion overlaps with the pros/cons of deploying a Web Garden for a specific application (2).

1)
http://support.microsoft.com/?id=325056
http://rodiniz.spaces.live.com/blog/cns!F2A56AAF89A7E43A!658.entry

2)
http://nicholas.piasecki.name/blog/2009/02/on-web-gardens-aspnet-and-iis-60/