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I have a react application and I would like to setup a websocket connection to my backend for some realtime updates. I was going to deploy an EC2 or ECS-cluster to host websocket connections. Then I stumbled into some articles showing how websocket connection can be setup in a serverless manner.

One example: https://medium.com/@likhita507/real-time-chat-application-using-webscockets-in-apigateway-e3ed759c4740

However, I can't seem to figure out how this works for a few reasons.

  • Lambda has a max runtime of 15 min
  • How does the backend establish a connection when no lambda is running and the backend wants to invoke a message to the frontend

Does this entail that I have to keep a lambda alive all the time, if so, it no longer feels like a good idea. In the above example, what I can't grasp is that when creating that chat application, can each chat room only exist for 15 min? And if a user disconnects from the room, how will that user be updated on new messages.

Does anyone have any experience with this kind of solution?

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It's the API Gateway that keeps the websocket connection alive. The browser (or whatever your client is) is connecting to the Gateway, not the lambda function.

The gateway triggers the Lambda function. You hook this up by selecting LAMBDA_PROXY from Integration Request. You can connect each route to a separate function, or have them all dealt with by one, whichever you prefer. Unless you're doing something very complicated in the function, it should only be executing for a few ms.

Communicating from the function to the original client is done through the gateway too - with APIGatewayManagementAPI.postToConnection (or you could roll your own http version using the connection URL I guess).

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