Suggestion GWT High Scale Application Server - java

Currently I am working on a Large Scale Application which uses GWT with Hibenate. We are facing some performance issues with existing Jetty / Tomcat server. And we want a another server that handles hibernate queries and GWT both perfectly.
Problem with tomcat is it sometimes stops responding GWT requests, and client hangs up on some points.
There are certain servers that comes in my mind like :
GlassFish
Jboss
IBM WebSphere AS
etc.
Please suggest some high scale server that handles GWT RPC request well and can run in multi-client environment well. We are expecting 100 concurrent users, Hardware is not an issue.
Thanking You,
Regards,

I think that your problem is not related to Tomcat or Hibernate. Your application should have scalebility problem. I do suggest you to investigate your application before investing to a fancy application server.

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Have you check for memory leakage in application as it is nothing to do with EC2 instance. As you mention it was working fine after restart.
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Okay so after some analysis (Thread dumping of my tomcat server on production) I found out that there were some processes (code-smells) which were taking all of my CPU space, and hence my instance was becoming slow, and effecting the performance of my application overall.

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Because the developers were all working on macOS and Windows and the issue only occurred on the acceptance and production environments which ran Ubuntu we incorrectly assumed this was the cause.
Lessons learned (these are all really dumb and basic but we made these mistakes anyway):
Be sure to validate all your assumptions! If we thought Ubuntu was the issue we should've singled out Ubuntu in tests earlier. For example, by using a VM with Ubuntu on which to validate our assumptions in quarantaine.
Make sure your development environment matches your production environment! In our development environments we weren't running haproxy. As "high level" developers we tend to put aside load balancers and web servers as commodity infrastructure but this example once again shows that these "commodities" can very directly impact the working of your application.

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As per your comment I understand that you created a web application with a Jetty embedded server.
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EDIT
Thanks to you I made a deeper research on the topic and found an interesting guide to deploy a web application with embedded Jetty server in Heroku. I've never tried it nor I know if its free, but maybe you can give a try.
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http://www.digitalocean.com
I know this is a touch redundant but I don't have voting or comment rights yet so this is the only method for me to communicate.
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Are there other alternative solution, such as using another hosting provider or use a different web server? (Because it is a startup, it would be beneficial if the answer keeps scalability in mind)
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See http://zeroturnaround.com/liverebel
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