Websocket API to replace REST API?

I learned a little lesson (the hard way). I made a number crunching application that runs on Ubuntu AWS EC2 cloud services (uses powerful GPUs), and I wanted to make a front-end for it just to watch its progress in realtime. Due to the fact that it needed realtime data, it was obvious that I needed websockets to push the updates.

It started with a proof of concept, and worked great. But then when we wanted to make it available to the public, we had to add user session, so we needed login features. And no matter how you look at it, the websocket has to know which user it deals with, so we took the shortcut of using the websockets to authenticate the users. It seemed obvious, and it was convenient.

We actually had to spend quiet some time to make the connections reliable. We started out with some cheap websocket tutorials, but discovered that our implementation was not able to automatically reconnect when the connection was broken. That all improved when we switched to socket-io. Socket-io is a must !

Having said all that, to be honest, I think we missed out on some great socket-io features. Socket-io has a lot more to offer, and I am sure, if you take it in account in your initial design, you can get more out of it. In contrast, we just replaced the old websockets with the websocket functionality of socket-io, and that was it. (no rooms, no channels, ...) A redesign could have made everything more powerful. But we didn't have time for that. That's something to remember for our next project.

Next we started to store more and more data (user history, invoices, transactions, ...). We stored all of it in an AWS dynamodb database, and AGAIN, we used socket-io to communicate the CRUD operations from the front-end to the backend. I think we took a wrong turn there. It was a mistake.

• Because shortly after we found out that Amazon's cloud services (AWS) offer some great load-balancing/scaling tools for RESTful applications.
• We have the impression now that we need to write a lot of code to perform the handshakes of the CRUD operations.
• Recently we implemented Paypal integration. We managed to get it to work. But again, all tutorials are doing it with RESTful APIs. We had to rewrite/rethink their examples to implement them with websockets. We got it to work fairly fast though. But it does feel like we are going against the flow.

Having said all that, we are going live next week. We got there in time, everything works. And it's fast, but will it scale ?

I would consider using both. Each technology has their merit and there is no one-size fits all solution.

The separation of work goes this way:

1. WebSockets would be the primary method of an application to communicate with the server where a session is required. This eliminates many hacks that are needed for the older browsers (the problem is support for the older browsers which will eliminate this)

2. RESTful API is used for GET calls that are not session oriented (i.e. not authentication needed) that benefit from browser caching. A good example of this would be reference data for drop downs used by a web application. However. can change a bit more often than...

3. HTML and Javascript. These comprise the UI of the webapp. These would generally benefit being placed on a CDN.

4. Web Services using WSDL are still the best way of enterprise level and cross-enterprise communication as it provides a well defined standard for message and data passing. Primarily you'd offload this to a Datapower device to proxy to your web service handler.

All of this happen on the HTTP protocol which gives use secure sockets via SSL already.

For the mobile application though, websockets cannot reconnect back to a disconnected session (How to reconnect to websocket after close connection) and managing that isn't trivial. So for mobile apps, I would still recommend REST API and polling.

Another thing to watch out for when using WebSockets vs REST is scalability. WebSocket sessions are still managed by the server. RESTful API when done properly are stateless (which mean there is no server state that needs to be managed), thus scalability can grow horizontally (which is cheaper) than vertically.

I'd like to point out this blog post that is up to me, the best answer to this question.

In short, YES

The post contains all the best practices for such kind of API.