Large number of WebSocket connections

Question

I am writing an application that keeps track of content pushed around between users of a certain task. I am thinking of using WebSockets to send down new content as they are available to all users who are currently using the app for that given task.

I am writing this on Rails and the client side app is on iOS (probably going to be in Android too). I'm afraid that this WebSocket solution might not scale well. I am after some advice and things to consider while making the decision to go with WebSockets vs. some kind of polling solution.

Would Ruby on Rails servers (like Heroku) support large number of WebSockets open at the same time? Let's say a million connections for argument sake. Any material anyone can provide me of such stuff?

Would it cost a lot more on server hosting if I architect it this way?

Is it even possible to maintain millions of WebSockets simultaneously? I feel like this may not be the best design decision.

This is my first try at a proper Rails API. Any advice is greatly appreciated. Thx.

Answer 1

Million connections over WebSockets, using Ruby, I can't see its real if you not using clustering to spread connections between different instances to handle all the data processing.
The problem here is serializing and deserializing data.

As well you have to research of how often you will need to pull data to client from server, and if it worth to have just periodical checks using AJAX, then handling connection for whole time. Because if you do handle connection and then you not using it - it is waste of resources. WebSockets are build on top of TCP layer, and all connections are not "cheap" as well going through for OS and asking them for data available again is not the simple process, with millions connections it is something really almost impossible without using most advanced technologies in the world.

I head that Erlang is able to handle millions of connections, but I don't have details over it. As well connection is one thing, another is processing data and interaction between connections - this you might want to check, because if you have heavy processing algorithms, then you definitely need to look into horizontal scaling options over clustering solutions.