Linux – java.io.IOException: Too many open files on tomcat server

I have web application which is based on JAVA (GWT Framework). I hosted my web application on Redhat Linux Server 6.0 using Tomcat 8.0.9 in front of apache http server connected using AJP connector and JDK 8. Whenever 20+ users access my website tomcat goes failed and that i checked the logs file i got this execption

19-Oct-2015 12:38:15.350 SEVERE [ajp-nio-8009-Acceptor-0] org.apache.tomcat.util.net.NioEndpoint$Acceptor.run Socket accept failed
 java.io.IOException: Too many open files
    at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
    at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:241)
    at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:688)
    at java.lang.Thread.run(Thread.java:745)

Web Application uses :

Database : couchdb 1.5 (Running on ec-2 machine using 4gb RAM)

Search : elasticsearch 1.0 (Running on ec-2 machine using 4gb RAM)

Tomcat : Tomcat 8.0 in front of apache server connected using ajp
connector(Running on ec-2 machine using 8gb RAM)

I searched alot & find out the solution to change the values of fs.file-max = 200000 and soft file and hard file limit to 65535 but still this error occur and tomcat stop responding. Then i need to restart the tomcat ec-2 machine then only application start running properly.

I could not understand why this problem occurs very frequently?

My clients get irritating because of this problem. Please help me out of this problem