From all the homework I have been doing in the last few days, I obtained the following information. Node.js
Some of the sources that I have come across are:
Considering that Node.js can be run almost out-of-the-box on Amazon's EC2 instances, I am trying to understand what type of problems require Node.js as opposed to any of the mighty kings out there like PHP, Python and Ruby. I understand that it really depends on the expertise one has on a language, but my question falls more into the general category of: When to use a particular framework and what type of problems is it particularly suited for?
You did a great job of summarizing what's awesome about Node.js. My feeling is that Node.js is especially suited for applications where you'd like to maintain a persistent connection from the browser back to the server. Using a technique known as "long-polling", you can write an application that sends updates to the user in real time. Doing long polling on many of the web's giants, like Ruby on Rails or Django, would create immense load on the server, because each active client eats up one server process. This situation amounts to a tarpit attack. When you use something like Node.js, the server has no need of maintaining separate threads for each open connection.
This means you can create a browser-based chat application in Node.js that takes almost no system resources to serve a great many clients. Any time you want to do this sort of long-polling, Node.js is a great option.
I look forward to reading other answers here, this is a fantastic question.
It's worth pointing out that Node.js is also great for situations in which you'll be reusing a lot of code across the client/server gap. The Meteor framework makes this really easy, and a lot of folks are suggesting this might be the future of web development. I can say from experience that it's a whole lot of fun to write code in Meteor, and a big part of this is spending less time thinking about how you're going to restructure your data, so the code that runs in the browser can easily manipulate it and pass it back.
Here's an article on Pyramid and long-polling, which turns out to be very easy to set up with a little help from gevent: TicTacToe and Long Polling with Pyramid.
I believe Node.js is best suited for real-time applications: online games, collaboration tools, chat rooms, or anything where what one user (or robot? or sensor?) does with the application needs to be seen by other users immediately, without a page refresh.
I should also mention that Socket.IO in combination with Node.js will reduce your real-time latency even further than what is possible with long polling. Socket.IO will fall back to long polling as a worst case scenario, and instead use web sockets or even Flash if they are available.
But I should also mention that just about any situation where the code might block due to threads can be better addressed with Node.js. Or any situation where you need the application to be event-driven.
Also, Ryan Dahl said in a talk that I once attended that the Node.js benchmarks closely rival Nginx for regular old HTTP requests. So if we build with Node.js, we can serve our normal resources quite effectively, and when we need the event-driven stuff, it's ready to handle it.