TypeScript CDK WebSocket with REST API and SDK@V3 Layer

A minimal WebSocket example stack. Resources created:

• API Gateway WebSocket API
• API Gateway REST API
• DynamoDB Table
• Lambdas and lambda layer

Lambda Layer

The lambda-layer/package.zip file needs to be created before deploying.

Bundled packages controlled by lambda-layer/nodejs/package.json

Run ./build.sh in the lambda-layer/ folder.

Source

Main stack in lib/websocket-stack.ts

Lambda code in src/

Testing

Chrome Simple WebSocket Client Extension: https://chrome.google.com/webstore/detail/simple-websocket-client/pfdhoblngboilpfeibdedpjgfnlcodoo

Connect to ${WebsocketStack.WebSocketStageUrl} with a WebSocket client.

Open ${WebSocketStack.BroadcastUri} in a browser.

You should see {"now":"2022-03-05T03:19:53.765Z"} in the WebSocket client but with the current date-time.

Send valid json from one client and all clients should see it. The input is only restricted to json due to _OnDefault using JSON.parse(event.body) before broadcasting.

Lambdas

• src/_OnConnect is called by the API Gateway WebSocket on connect. Returning an error prevents the connection.
• src/_OnDisconnect is called by the API Gateway WebSocket on disconnect.
• src/_OnDefault is called by the API Gateway WebSocket as the default route handler if routeSelectionExpression does not resolve to another handler. In this example it just broadcasts any valid json to all connections.

Note

WebSocket connections have a 10 minute idle disconnect and a 2 hour maximum connection time.

Useful commands

• npm run build compile typescript to js
• npm run watch watch for changes and compile
• npm run test perform the jest unit tests
• cdk deploy deploy this stack to your default AWS account/region
• cdk diff compare deployed stack with current state
• cdk synth emits the synthesized CloudFormation template