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What are optimal settings for Recycling of Application Pools in IIS7 in a shared environment?
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By default, an IIS application pool (or “AppPool”) recycles on a regular time interval of 1740 minutes, or 29 hours. One reason for this time interval is that application pools don't recycle at the same moment every day (every day at 07.00 for example).
Worker process isolation mode offers process recycling, in which IIS automatically refreshes Web applications by restarting their worker processes. Process recycling keeps problematic applications running smoothly, and is an especially effective solution in cases where it is not possible to modify the application code.
The 1740 story Wade suggested 29 hours for the simple reason that it's the smallest prime number over 24. He wanted a staggered and non-repeating pattern that doesn't occur more frequently than once per day.
As a Hoster, you definitely want to recycle on Memory & Time, potentially Request limits and CPU. You want to be pretty aggressive about these limits, but make sure you publish them to your clients.
Memory - 512 for an x86 box, maybe 768. For x64, you can set this much higher depending on the number of hosts per server. You just have to be careful and watch your app pool recycle events on memory issues.
Time - We typically recycle at 1 am in the morning, plus or minus (first site 1:01, second 1:11, third 1:21, just so you don't have all recycling at the same time)
Request limit - 35,000 was the default for IIS6, but this number is quite arbitrary, and very dependant on the site in question. For small usage sites, the nightly recycle will hit long before you get 35k requests.
CPU - 95%/1 minute limit/KillW3WP, but use this carefully. My understanding of this is that if the CPU hits 95%+ over the 1 minute limit for this worker process, the worker process gets killed and is unable to restart for the remainder of the limit when Action is set to KillW3WP. You might want to try NoAction initially and just watch your event logs carefully.
Recycle Event Logs - You want to make sure you are logging app pool recycles for each event threshhold that you set - i.e. if you limit based off of requests limits, make sure that Request Limit logging is enabled.
One thing to remember is that you should set retail="true" in the <deployment> element in your machine.config:
<system.web> <!-- <deployment retail = "false" [true|false] /> --> <deployment retail="true" /> </system.web> Not setting this will allow a site to turn debugging on, which allows unlimited timeouts in requests - not exactly ideal for a hoster...
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Tip: When you recycle your app, all your session variables are destroyed... so caution on this!
IMHO, keep the defaults.
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