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Reconnecting websockets on AWS

In this example, we set up reconnecting websocket solution with API Gateway, DynamoDB and Lambda using Serverless Framework written in Python.

Read this blogpost for a more in depth explaination of how this works.

Pre-requisites

In order to deploy the application, you will need the following:

API credentials for AWS, with Administrator permissions (for simplicity, not recommended in production). Node.js and npm / pnpm / yarn installed locally.

Deploying the project

  1. Clone the repository
  2. Install node dependencies: npm i
  3. Deploy backend: sls deploy --verbose
  4. Deploy frontend: npm run dev

So how does this work?

Persistent WebSockets generally require:

  • A shared ID between both server and client - Eg: Session Key or other Auth info - "socketID" in our case.
  • A Key Value with Pub Sub capability - Eg: Redis - DynamoDB in our case

Connecition workflow:

  1. First send an empty "socketID" via the WebSocket to indicate that no persistent connections exist - via "open" route.
  2. In new persistent connections "socketID" is defined by the server.
  3. On every connection, a new "connectionId" is created by API Gateway and saved to DynamoDB with associated "socketID".
  4. The DynamoDB stream allows "socketID" to proxy "connectionId". Any updates will trigger a lambda to send updated messages to the client via "connectionId".

Note: Route is an API Gateway specific concept that needs to be configured.