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WebSockets on AWS API Gateway

WebSocket-based APIs are bidirectional in nature. This means that a client can send messages to a service and services can independently send messages to its clients.

This bidirectional behavior allows for richer types of client/service interactions because services can push data to clients without a client needing to make an explicit request.

WebSocket APIs are often used in real-time applications such as chat applications, collaboration platforms, multiplayer games, and financial trading platforms.

routeKey in API Gateway

There are three special routeKey values that API Gateway allows you to use for a route:

  • $default: Used when the route selection expression produces a value that does not match any of the other route keys in your API routes. This can be used, for example, to implement a generic error handling mechanism.
  • $connect: The associated route is used when a client first connects to your WebSocket API.
  • $disconnect: The associated route is used when a client disconnects from your API. This call is made on a best-effort basis.

Part1: Create WebSockets in API Gateway

In the API Gateway console, create a new api:

  1. select WebSocket

  2. API name: wsEcho

  3. Route selection expression: $request.body.action

  4. Description: echo websocket information

  5. Add new route key echo to handle $request.body.action

We will park here. Create lambda functions to handle different routes.

Part2: IAM lambda execution role

Create lambda_basic_execution_role:

  1. In IAM console, click on create role.

  2. Select Lambda service

  3. Policies:

    • AWSLambdaBasicExecutionRole
    • AWSLambdaVPCAccessExecutionRole
    • AmazonAPIGatewayInvokeFullAccess

Create apigw_cloudwatch_log:

  1. service: api gateway

  2. policy: AmazonAPIGatewayPushToCloudWatchLogs

  3. copy the arn and put in the api gateway setting to enable cloudwatch log.

Part3: Lamdba functions to handle routes

Setup SAM packages in cloud9

  1. Create a cloud9 environment

  2. click on AWS Resources and then create a local lambda function

  3. Setup the Applicaiton and Lambda Function

    • Application name: webSocketsOnAPIGW
    • Function name: wsEcho
    • runtime: node.js 6.10
    • blueprint empty-nodejs
    • Function trigger: none
    • Role: select existing role: lambda_basic_execution_role

  4. In the right panel, right click on webSocketsOnAPIGW and select Create Here:

    • Function name: wsConnect, wsDisconnect, and wsDefault
    • runtime: node.js 6.10
    • blueprint empty-nodejs
    • Function trigger: none
    • Role: select existing role: lambda_basic_execution_role

  5. Modify template.yaml

    • All runtime: nodejs8.10

    • change hander name:

      • Handler: wsEcho/echo.handler
      • Handler: wsConnect/connect.handler
      • Handler: wsDisconnect/disconnect.handler
      • Handler: wsDefault/default.handler

    • You can reference template.yaml sample

  6. Rename index.js file name to the meaningful file names:

    • wsEcho/echo.js
    • wsConnect/connect.js
    • wsDisconnect/disconnect.js
    • wsDefault/default.js

Write websocket handler function

  1. Copy the source code to related files:

  2. Create a package.json:

  3. In the cloud9, open a new terminal. Go to wsEcho to install related package.

    • cd webSocketsOnAPIGW/wsEcho/
    • npm i

  4. Right click on webSocketsOnAPIGW, then deploy.

  5. In lambda console, you will see the functions. If error, please check the cloudformation for detail information.

Part3: Bind API Gateway with Lambda

  1. Click on the Integration Request for the echo routes. Then bind to echo lambda function.

  2. follow the same process to bind $connect, $disconnect, and $default.

  3. Click on the Actions then deploy api to stage dev

  4. Copy the web socket end points. Setting Logs/Tracing.

Part4: Verify

  1. In cloud9, npm install -g wscat

  2. Then, in the cosonle, use the command

    wscat -c wss://<endpoint-id>.execute-api.us-east-1.amazonaws.com/dev

  3. Check cloud watch for api and lamdba.

Reference