From a load generation standpoint, it is almost irrelevant what technologies your server is using. The only thing you really care about is the method of communication between client and server, as you will need to simulate many clients using your load test tool of choice. OpenSTA does HTTP (and SSL) only, so if you are testing a web application, it will work perfectly, since HTTP is the protocol you are interested in. JMeter would also work in that case (although OpenSTA is much more scalable).
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