Serverless Websocket — How and Why With Examples | by Emil Hein | May, 2022

Why would you need to use a WebSocket connection and may we make it serverless?

AWS WebSockets and the serverless framework


The sort of connection between consumer and server isn’t particularly new. It has traditionally been a bit of difficult to work with, and it might need scared some individuals away from utilizing it.

Briefly, a WebSocket is a unique paradigm that the same old request-response sample that powers most the common web sites. As an alternative, WebSocket creates a bidirectional connection between a server and a consumer. Which means the server can now actively push messages to a consumer, which may make an enormous distinction in some use instances.

Regular instance use instances could possibly be

  • Actual-time chatting
  • “Who’s watching” performance
  • Person to consumer interplay


I’m an enormous fan of the serverless framework because it permits me to simply arrange a backend useful resource, with out pondering an excessive amount of of the underlying infrastructure. This creates a pleasant abstraction, that makes it very straightforward and enjoyable to prototype issues.

Now, in relation to WebSockets, we’re restricted by the cloud suppliers’ choices. I will probably be utilizing AWS, and due to this fact will probably be the AWS Lambda perform that can act because the server and API Gateway that can present the WebSocket characteristic.

This brings with it, some limitations. In response to the docs the Idle restrict is, by the point of writing, set to 10 minutes. Which means when the consumer initiates the connection, the connection will probably be disconnected routinely after 10 minutes if no occasions are despatched both means.

In excessive instances, the payload restrict and connection fee restrict may additionally make the API Gateway a non-option.

One other consideration is the pricing. For the reason that serverless paradigm isn’t lower out to serve lengthy connection and long-running features. For that, the pricing is just too costly. When utilizing API Gateway you pay per message transferred and “connection minutes”. Which means the longer the consumer is related with the API Gateway (and lambda), the extra you pay. So if you could do very lengthy workflows I’d say that you simply’re means higher of, utilizing a “actual” server (EC2 within the AWS case)

I did nonetheless just lately discover a use case the place each WebSockets and the serverless paradigm may work collectively to create an answer.

Use case

We’ve got a set of assessments a consumer can provoke. The consumer doesn’t and will know precisely which take a look at when initiating them. These assessments are dynamic and may fluctuate from taking 1 second as much as 40–50 seconds and in some instances much more. Within the real-life use case, these assessments would crawl a web page and do sure assertions and checks.

Here’s a redacted screenshot of the dwell use case:

WebSocket assessments


Not a lot loopy happening within the serverless setup file.
The one factor to notice is that we right here have 3 handlers:

  • A connection handler that can deal with the preliminary connection setup.
  • A disconnect handler that could possibly be used to scrub up sources if a consumer disconnect
  • A default handler that the consumer will ship messages and obtain messages from


For the backend (the lambda handler) we’ll implement a reasonably easy WebSocket characteristic for our use case.

This instance will begin 3 “assessments” that resolve after some seconds. That is for example how every process would possibly take longer. This could possibly be if HTTP requests are concerned or heavy computation:

And the taskrunner.js perform seems like this

The helpers’ strategies appear like this:

With the above 3 items, we will now assemble a easy instance to check if WebSockets are a viable option to resolve the use case

The above code will run via 3 duties that can every ship some messages to the consumer through the websocket connection. Let’s have a look at it in motion:

The challenge in motion

The complete code instance may be discovered here.

As talked about above, the WebSocket paradigm doesn’t match significantly properly with the serverless paradigm. Particularly pricing will issue to look out for. Nonetheless, I do consider that the advantages of each serverless and WebSocket have a set of use instances the place the mixture of the 2 may be highly effective.

With serverless, we keep away from the overhead of really managing a server. In some instances, a “actual” server will nonetheless be your best option although. With WebSockets, we will some capabilities, that might be very troublesome (generally not possible) to do with a standard request/response.

Later I’ll present how we will join a Vue 3 utility in order that our new WebSocket capabilities will come actually alive.

Keep related.

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