How to access monitoring web UI when running spark on AWS

I'm running spark from AWS EC2. As the spark documentation said

"Each driver program has a web UI, typically on port 4040, that displays information about running tasks, executors, and storage usage. Simply go to http://:4040 in a web browser to access this UI"

My question is: what is this "driver-node"? I thought it's the public IP of the driver node xx.xx.xxx.xx. But I kept getting page not found error when I user http://ift.tt/1T9erME

Please help.