Getting bandwidth spent by user or by rails application on Ubuntu

Question

I'm running multiple rails applications on AWS instance and I need to know how many bandwidth is each application using/wasting.

Some of the applications are running with passenger over Apache2 some of them are running over Passenger standalone server and some of them are running on WebRick standalone server.

Also each application is located under a corresponding home user directory, because we've created a user for each project.

Now, can I get the bandwidth usage for each user and log it to text files o even directly to my database?

Or can I get the bandwidth usage for each Ruby on Rails application running?

I have already used the iptraf command line utility but it was on one sever hosting one single rails application and just got to log the traffic on one interface, now I need to have the usage by user or by application.

Any help?

Thanks.