Javascript – Is it possible to receive an Amazon SNS message on a JS script

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.

It's worth mentioning that Ruby and Python both have tools to do this sort of thing (eventmachine and twisted, respectively), but that Node.js does it exceptionally well, and from the ground up. JavaScript is exceptionally well situated to a callback-based concurrency model, and it excels here. Also, being able to serialize and deserialize with JSON native to both the client and the server is pretty nifty.

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.

SNS is a distributed publish-subscribe system. Messages are pushed to subscribers as and when they are sent by publishers to SNS.

SQS is distributed queuing system. Messages are not pushed to receivers. Receivers have to poll or pull messages from SQS. Messages can't be received by multiple receivers at the same time. Any one receiver can receive a message, process and delete it. Other receivers do not receive the same message later. Polling inherently introduces some latency in message delivery in SQS unlike SNS where messages are immediately pushed to subscribers. SNS supports several end points such as email, SMS, HTTP end point and SQS. If you want unknown number and type of subscribers to receive messages, you need SNS.

You don't have to couple SNS and SQS always. You can have SNS send messages to email, SMS or HTTP end point apart from SQS. There are advantages to coupling SNS with SQS. You may not want an external service to make connections to your hosts (a firewall may block all incoming connections to your host from outside).

Your end point may just die because of heavy volume of messages. Email and SMS maybe not your choice of processing messages quickly. By coupling SNS with SQS, you can receive messages at your pace. It allows clients to be offline, tolerant to network and host failures. You also achieve guaranteed delivery. If you configure SNS to send messages to an HTTP end point or email or SMS, several failures to send message may result in messages being dropped.

SQS is mainly used to decouple applications or integrate applications. Messages can be stored in SQS for a short duration of time (maximum 14 days). SNS distributes several copies of messages to several subscribers. For example, let’s say you want to replicate data generated by an application to several storage systems. You could use SNS and send this data to multiple subscribers, each replicating the messages it receives to different storage systems (S3, hard disk on your host, database, etc.).