Jboss as 7 minimum hardware requirements are quite small, but It all depends on your usage.
For demo purposes take a look at jboss world 2011 keynote which ran on plug computer with 512MB of ram and 1Ghz arm CPU.
for more details look at
In short hardware requirements are really low, but it all depends on what are your application needs.
The main requirement is that you have JDK 6 or 7 and that is about it. any system that runs that is good enough.
Default configuration of server takes around 15mb(32bit JVM) of memory when it is up, but this goes up with your application.
Any CPU that is less that 5 years old would be fine, but there isn't any special requirement on that.
Do you have any special requirement that you are worried about?
What about running a very simple CRUD web app on Amazon EC2. (lets suppose one visitor per several seconds, max 3 users concurrently)
I know it depends, but Will it run in a Micro Instance? What about a Small? Maybe a Medium?
Any guidelines are much appreciated.
There should be no issues running AS7 on EC2 micro instance and it should work just fine.
given that your application is not really memmory hungry
I personaly use EC2 micro instances with AS7 with no issues.
I would recomend you using 32bit AMIs for micro instances so you can have more memmory for yourself(app)
Then a small instance, x64 should run a small app with no problem.