We are deploying first website on Jboss.The no of users of the website are between 800-900.But it wont be a busy site.(I guess number of users accessing same time are no more than 10.) Hows the performance of JBOSS in this scenario without clustering? Do I need to do clustering in Jboss? Also if I do clustering will that affect my code too? What needs to be changed in the code if at all I need clusetring.
It really depends on how heavy the the load of those 10 simultaneous users is going to be and that depends on how you've designed your web application.
Does this Web Application do its heavy processing:
1.) On the database? 2.) On the mid tier? 3.) On the front end?
For a bog standard, reasonably designed web site using fairly standard server hardware specs I'd say that you wouldn't have to cluster JBoss for 10 users (it's pretty good at resource management).
This also assumes you don't need or want to cluster JBoss in terms of DR.
This also assumes your simultaneous user base isn't going to grow significantly in the future.
If you did have to cluster then yes you'd have to make sure you application design/code could handle being clustered, but that's a whole new topic
A good tool to test the performance is JMeter. I'd try running 10 then 100 simultaneous threads mimicking your users against a Jboss instance in a test environment and see what the performance is like!