WebSocket APIs for Real-Time Communication
Build two-way, real-time connections with API Gateway WebSocket APIs. Learn the connect, disconnect, and message routes and how to push data back to clients.
WebSocket APIs for Real-Time Communication is a free Serverless Backend with AWS Lambda & API Gateway lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Serverless Backend with AWS Lambda & API Gateway learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why WebSockets?
REST APIs are request/response — the server cannot push. For chat, live dashboards, or notifications you need a persistent two-way channel. API Gateway WebSocket APIs provide exactly that.
The Three Built-in Routes
A WebSocket API has special routes:
$connectwhen a client connects$disconnectwhen it leaves$defaultfor unmatched messages
Route Selection Expression
Custom routes are chosen by a route selection expression, usually a field in the incoming JSON such as $request.body.action.
{
"action": "sendMessage",
"data": "hello"
}Handling $connect
The $connect handler receives a unique connectionId. Store it (e.g. in DynamoDB) so you can message that client later.
exports.handler = async (event) => {
const id = event.requestContext.connectionId;
await save(id);
return { statusCode: 200 };
};Handling $disconnect
On disconnect, remove the stored connectionId so you do not try to message a dead client.
exports.handler = async (event) => {
await remove(event.requestContext.connectionId);
return { statusCode: 200 };
};Pushing Messages to a Client
To send data back, call the management API with the target connectionId.
const api = new ApiGatewayManagementApi({ endpoint });
await api.postToConnection({
ConnectionId: id,
Data: JSON.stringify({ msg: "hi" })
});Broadcasting to Many Clients
To broadcast, loop over all stored connectionIds and post to each. Remove any that return a 410 Gone status — those clients have disconnected.
Authorizing Connections
Attach a Lambda authorizer to the $connect route to validate a token before the connection is accepted, rejecting unauthorized clients up front.
Connection Lifetime and Limits
WebSocket connections last up to 2 hours, with a 10-minute idle timeout. Clients should reconnect when dropped, and you should handle stale connectionIds gracefully.
Pricing Model
You pay for messages transferred and for connection-minutes, not for idle request count. This makes WebSocket APIs cost-effective for bursty real-time traffic.
When to Use WebSockets
Reach for WebSocket APIs when you need:
- Live chat or collaboration
- Real-time dashboards
- Server-initiated notifications
For simple request/response, stick with REST or HTTP APIs.
Quick Check
Test your WebSocket API knowledge.
Recap
You learned real-time APIs:
- WebSocket APIs add two-way communication
$connect,$disconnect,$defaultplus custom routes- Store connectionIds and push via postToConnection
- Authorize on $connect; handle stale connections
Frequently asked questions
Is the “WebSocket APIs for Real-Time Communication” lesson free?
Yes — the full text of “WebSocket APIs for Real-Time Communication” is free to read here on the web, and the Serverless Backend with AWS Lambda & API Gateway course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Serverless Backend with AWS Lambda & API Gateway course, upgrade to CoddyKit PRO.
What will I learn in “WebSocket APIs for Real-Time Communication”?
Build two-way, real-time connections with API Gateway WebSocket APIs. Learn the connect, disconnect, and message routes and how to push data back to clients. You practise Serverless Backend with AWS Lambda & API Gateway with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Serverless Backend with AWS Lambda & API Gateway?
No prior experience is required. Serverless Backend with AWS Lambda & API Gateway on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “WebSocket APIs for Real-Time Communication” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Serverless Backend with AWS Lambda & API Gateway lesson?
Yes. Every Serverless Backend with AWS Lambda & API Gateway lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Caching and Throttling
- Request/Response Transformations
- Custom Domain Names & Edge Optimization
- WebSocket APIs for Real-Time Communication