Separate application pools for ASP.net applications in IIS

Question

I\'ve read recommendations that we should create separate application pools for each asp.net application on our Win2008 server.

We have about 20 apps that would be on t

Answer 1

Separating apps in pools is a good thing to do when there's a reason, and there are a number of good reasons listed above. There are, however, good reasons not to separate apps into different pools, too.

Apps using the same access, .NET version, etc. will run more efficiently in a single pool and be more easily maintained. Most annoyingly, IIS will kill idle app pools, requiring the pool be recreated on each use. If you isolate infrequently used apps you'll impose an unnecessary startup cost on users. Combining these apps into a single pool will make for happier users when they don't pay the startup cost, happier servers when they don't give memory to multiple processes and CPU slices for them, and happier admins when they have to manage fewer app pools.

Answer 2

I used to have 58 .Net websites and 17 old classic ASP websites on the same IIS7.5 server using separate app pools for each site. I noticed that the IIS compression started failing intermittently, causing the style sheets to be corrupted about 5% of the time. Looking at the task manager on the server, I could see that the server was approaching it's 4GB ram limit- each w3wp.exe process was taking anything up to 100 MB memory depending on how much traffic the site was getting. I then moved all the websites into just 2 application pools (one for .net 4 websites and one for the old classic ASP sites) and the total memory used after doing that dropped from 3.8GB to just under 2.8GB - saving me over 1GB memory space on the server. After the change (and leaving the server running for a couple of hours to get back to normal levels of traffic), the w3wp processes were using 300MB for all the .net websites websites and 20MB for the classic ASP websites. I could re-enable IIS compression again without a problem.

Using separate APP pools is a great idea for many of the reasons mentioned by the other posts above, but it also in my experience causes a much higher memory overhead if you are hosting a fair number of websites on the same server.

I guess it's a trade-off between hardware restrictions and security whether you want to use separate app pools. It's a good idea if you have the resources to do it.

Answer 3

The main benefit of creating different application pools is that you can provide each pool with other credentials. Your 20 applications may communicate with 20 different databases that all need another login. The best practice then is to run each application using a different service account.

I wouldn't worry too much about performance. Most time will probably be spent inside each web application, no matter what process each application is in.