Session handling across the nodes and web server

Hi experts, 

I am working in an AEM app which does following -

1. User submits the data through AEM forms
2. We collect the data in AEM form action jsp and make a string 
3. We store string in a session (HTTP session i.e. session.setAttribute )
4. AEM redirects user to a thank you page
5. We have a “Call to action” on thank you page
6. On this call to action, we hit a backend JSP say”createfile.jsp” that reads the string from session variable and create a text file to download (session.getAttribute)

This works in single nodes (like author, publish etc), but when I am dealing with the web server it doesn’t. I am not able to collect the session data.  I have 2 author, 2 pub nodes and 1 web server.

Here is the form action script

submiForm.jsp

<%

String str=request.getParameter("bnfname4");

request.getSession().setAttribute("data", str);

%>

Here is the createfile.jsp

<%

String txt=(String)request.getSession().getAttribute("data");

%>

Any idea??