[AWS] WebSockets with API Gateway

Websocket is a bit different from HTTP, they work on top of a TCP connection.

User connects to API Gateway with some payload, Apigateway routing the request to different Lambda functions:

 

There are some special routes defined for websockets,

• `$connect`: When user connect to API Gateway thought websocket
• `$disconnet`:
• `$defualt`: default one, when there is no matching route

 

API Gateway WebSocket URL

WebSocket API provides two URLs: WebSocket URL and Connection URL.

WebSocket URL:

• Clinent use to connect to API
• Allows clients to send message and receive notifications

Connection URL:

• Send back message to client
• Lambda function use it to send message
• Requires a connection id to send a message to particular client

Connection id will be stored in DynamoDB table, a lambda function will read from it.

 

Connection URL supports the following operations:

• POST: to send a message to a client
• GET: to get the latest connection status
• DELETE: to disconnect a client from API

Here is an example of how to react to WebSocket events using Serverless Framework:

ConnectHandler:
    handler: src/websocket/connect.handler
    events:
      - websocket:
          route: $connect

  DisconnectHandler:
    handler: src/websocket/disconnect.handler
    events:
      - websocket:
          route: $disconnect

Installing Tool

npm install wscat -g

wscat -c wss://52zeaf29d.exeute-api.eu-central-1.amazonaws.com/dev