Some code to throttle rapid requests to your CF server from one IP address
Note: This blog post is from 2010. Some content may be outdated--though not necessarily. Same with links and subsequent comments from myself or others. Corrections are welcome, in the comments. And I may revise the content as necessary.Some time ago I implemented some code on my own site to throttle when any single IP address (bot, spider, hacker, user) made too many requests at once. I've mentioned it occasionally and people have often asked me to share it, which I've happily done by email. Today with another request I decided to post it and of course seek any feedback.
It's a first cut. While there are couple of concerns that will come to mind for some readers, and I try to address those at the end, it does work for me and has helped improve my server's stability and reliability, and it's been used by many others.
Update in 2020: I have changed the 503 status code below to 429, as that has become the norm for such throttles. I had acknowledged it as an option originally. I just want to change it now, in case someone just grabs the code and doesn't read it all or the comments. Speaking of comments, do see the discussion below with thoughts from others, especially from James Moberg who created his own variant addressing some concerns, as offered on github, and the conversation that followed about that, including yet another later variant.
Update in 2021: Rather than use my code, perhaps you would rather have this throttling done by your web server or another proxy. It is now a feature offered in IIS, Apache, and others. I discuss those in a new section below.
Background: do you need to care about throttling? Perhaps more than you realize
Ever need to do a search for files with some given text (or files of a given name) in Windows? I realize you may use a favored file editor to do it, or (worse) may rely solely on the anemic Windows find. I'd like to point you to an awesome and free alternative. 
The tool presents the data aggregated over time, so you can view it per hour, day, week, etc. Great for both drilling down to find hot spots, and for viewing how coding/config improvements (resulting from your responding to the analyses) have led to performance improvements over time. 
The tool runs with low overhead: it reads data that the DB provides, storing it in a database and providing a web-based interface to view that data. The process to read the data and create the repository (and present the web-based interface) can (and should) be done on a server separate from the server being monitored. 
I wanted to share this observation with anyone else who may be suffering the problem--and perhaps not even realize it. I've had a couple of instances where I've noticed that in Outlook (2007, though perhaps in 2003), when I use Advanced Find (ctrl-shift-f) to search my mailboxes, folders, calendars, tasks, or such, it sometimes hasn't found something I know is there. 
