Determining website capacity
A client of mine has a website and they need to determine how "scalable" the site is currently. By this I mean the number of users browsing the site at the same time.
This is a common e-commerce application in .net not written by me and the code ... well lets just say, a little dubious.
A much larger company wants to buy them / throw funding their way, but they need some kind of metric to show how much load it can take before it falls apart. This large company has the ability to "turn faucets" into a huge user base - and obviously doesn't want to if the site crashes with traffic sneezing.
What is a good metric to provide here? And how can I get it?
Edit: updated question
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You would be better off doing a load test as it might give you more information about real world scenarios (something like http://www.scl.com/software-quality/hosted-load-test , no experience with them, though).
Also: scalability as far as I know, not how many concurrent users can be served, but how easy it is to serve more as the site gets bigger (by adding more servers, etc., how easy it is for the website to scale. does the codebase allow for unlimited servers, etc.)
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I always use Apache tool "ab": link text
Run it from another machine, preferably a BSD or Linux machine with no firewall rules that limit the tool's performance. Because otherwise the result may not be as reliable. If you are using a Windows computer, make sure you are using one that does not limit the number of active TCP connections.
When using "ab" the number you are looking for is "Requests per second". Experiment with the concurrency switch to see how many concurrent users you can handle before you get a lot of errors or when requests per second drop quickly.
If you notice that the web server is having serious problems, you should restart the web server and let it rest for a while before continuing testing.
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Well, I suppose it will depend on what the client cares about.
Do they care about how many users can immediately access the site? Please report this, but do concurrent requests from the other server until it dies and then get the number.
Does he care about something else?
For me, when someone says they want to "scale" it really means they have no idea what they want. So try talking to them and get specific information about what exactly they want to see "scaling", and then when you find areas to analyze, you can do it trivially and try to improve them.
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