API Gateway WebSocket: Real-Time Communication at Scale (2025 Guide)

Introduction to API Gateway WebSocket

What is API Gateway WebSocket?

Key Components of API Gateway WebSocket

WebSocket Routes and Route Selection Expressions

1{
2  "routeSelectionExpression": "$request.body.action"
3}
4

Integrations: Lambda, DynamoDB, HTTP

Predefined and Custom Routes ($connect, $disconnect, $default)

• $connect: Handles new connection events.
• $disconnect: Handles connection terminations.
• $default: Handles unmatched routes or messages.

Setting Up an API Gateway WebSocket API

Creating a WebSocket API via Console and CLI

AWS Console

1. Navigate to Amazon API Gateway.
2. Choose “Create API”, then select “WebSocket”.
3. Define the route selection expression (e.g., $request.body.action).
4. Add routes (e.g., $connect, $disconnect, custom routes).
5. Set up integrations (Lambda, HTTP, etc.).
6. Deploy the API to a stage.

AWS CLI Example

1aws apigatewayv2 create-api \
2  --name "ChatWebSocketAPI" \
3  --protocol-type WEBSOCKET \
4  --route-selection-expression "$request.body.action"
5

Defining Routes, Integrations, and Deployments

1{
2  "RouteKey": "onMessage",
3  "Target": "integrations/<lambda-integration-id>"
4}
5

Security Best Practices

Scaling and Managing WebSocket Connections

Challenges in Scaling WebSocket with API Gateway

Using API Gateway with EKS and KEDA

Connection Management and Monitoring

Invoking and Interacting with API Gateway WebSocket

Using wscat and WebSocket Libraries

1wscat -c wss://your-api-id.execute-api.region.amazonaws.com/production
2

1const ws = new WebSocket('wss://your-api-id.execute-api.region.amazonaws.com/production');
2ws.onmessage = (msg) => console.log(msg.data);
3

Sending Data from Backend to Client (@connections API)

1const AWS = require('aws-sdk');
2const apigw = new AWS.ApiGatewayManagementApi({
3  endpoint: 'https://your-api-id.execute-api.region.amazonaws.com/production'
4});
5
6const params = {
7  ConnectionId: event.requestContext.connectionId,
8  Data: JSON.stringify({ message: 'Hello, client!' })
9};
10
11await apigw.postToConnection(params).promise();
12

Handling Binary Data and Error Cases

Real-World Example: Serverless Chat Application

Serverless Chat with API Gateway WebSocket (2025)

• API Gateway WebSocket managing client connections and message routing
• AWS Lambda handling message processing and broadcasting
• DynamoDB tracking active users and chat history

Best Practices and Common Pitfalls

• Use fine-grained IAM policies and custom authorizers for security
• Monitor and enforce connection limits to prevent abuse
• Scale backend integrations (Lambda, DynamoDB) proactively
• Use connection IDs and DynamoDB TTL for state management
• Avoid using WebSocket for one-way or infrequent updates (consider REST)
• Test with tools like wscat and automate integration monitoring

Conclusion