I am not too clear about the IIS lifecycle, but my general understanding is:
- Every couple of hours IIS resets itself. This is apparently done so as to fix up any memory leaks, resource deadlocks etc. etc. ie. It seems to be a cleanup operation.
- Every couple more hours (I think I read 23 hours) the server just stops listening to inbound requests and runs Application_End. An external page request will restart the app.
Can I get a bit more reasoning to why these behaviors occur? Especially with regards to item #2… My server runs internal scheduling behaviors which completely died last night. The reason was that Application_End occurs and no customer requests were happening to start the IIS server again. This seems weird. Why not just clean up memory leaks etc. and then keep IIS running exactly as it was? The only reason I can think of is that it lets the server reclaim memory/cpu used by IIS, but that seems nonsensical and the cause of bugs, such as my scheduler issue!
I think the other posters have already answered your main question sufficiently well however I’d like to address the final part of your question.
and
Let’s think about the following scenario and what would happen if IIS behaved in this way. If we have a machine hosting several thousand websites (i.e. your typical shared hosting environment) each website has it’s own application pool (w3p.exe) running. Say that IIS started up a worker pool for each website regardless of if a request to that site had been made, you’d have a few thousand processes starting up at once each idling at say 2MB of RAM. If you’ve got 2000 websites you’ve just allocated 4GB of RAM to sit and essentially do nothing and the OS might start eating into the page file without any real need.
Is this desirable? I think you’d agree that the answer is no.