This is how-to run a proxy and see the WebUI of Namenode and Jobtracker of EC2 instances in the Hadoop (CDH4) cluster.

Configure proxy for Namenode and JobTracker WebUI

Now, Launch Firefox (3.0v+)
Download the FoxyProxy extension by clicking this link:https://addons.mozilla.org/en-US/firefox/addon/2464.
Steps to configure and access the UI
Select Tools > FoxyProxy > Options
Click the “Add New Proxy” button.
Select “Manual Proxy Configuration”
Enter “localhost” for the “Host or IP Address” field.
Enter “6666″ for the “Port” field.
Click on the “General” tab at the top of the dialog box.
Enter “EC2″ for the “Proxy Name” field.
Click on the “URL Patterns” tab at the top of the dialog box.
Click the “Add New Pattern” button.
Enter “EC2″ for the “Pattern Name” field.
Enter “*compute-1.amazonaws.com*, *.ec2.internal*, *.compute-1.internal*” for the “URL pattern” field (not case sensitive)
Select the “Whitelist” and “Wildcards” radio buttons.
Click the “OK” button to dismiss the new URL pattern dialog box.
Click the “OK” button to dismiss the new proxy dialog box.
Completely disable the Foxyproxy for now.
You should be able to see 2 proxy names after closing, default and EC2.
Click on “Use proxy EC2 for all URLs” from the pop-up menu of FoxyProxy
Copy the URL of JobTracker (can be seen while running proxy, ec2-***-**-***-**.********.amazonaws.com)  and paste it in the browser.