Polling vs WebSockets with AWS API Gateway: A Complete Guide
In modern application development, delivering real-time updates to users is often a requirement. Whether it's a chat application, a live sports dashboard, or a collaborative editing tool, users expect immediate feedback. When building these applications on AWS, specifically using Amazon API Gateway, you generally have two architectural patterns to choose from: Polling and WebSockets.
This guide explores the differences, benefits, and trade-offs of each approach to help you make the right decision for your architecture.
<h2 id="what-is-polling">What is Polling?</h2>Polling is the traditional method where the client repeatedly requests data from the server.
Short Polling
In short polling, the client sends a request at a fixed interval (e.g., every 5 seconds). The server responds immediately, either with new data or an empty response if nothing has changed.
- Pros: Simple to implement, works with standard HTTP/REST APIs.
- Cons: High overhead (HTTP headers per request), latency (updates are only as fast as the interval), wasted resources on empty checks.
Long Polling
Long polling improves on this by holding the client's request open until new data is available or a timeout occurs.
- Pros: Lower latency than short polling, fewer empty responses.
- Cons: Server resources are tied up holding connections, client logic is slightly more complex.
WebSockets provide a persistent, bi-directional communication channel between the client and the server over a single TCP connection. Once established, either side can send data at any time.
- Pros: Extremely low latency, low overhead (no HTTP headers per message), efficient for high-frequency updates.
- Cons: Stateful connection management, potentially more complex infrastructure (though AWS manages much of this).
Amazon API Gateway supports both patterns natively:
- REST/HTTP APIs (for Polling): You can build standard endpoints that clients poll. This integrates seamlessly with AWS Lambda or other backends.
- WebSocket APIs: API Gateway manages the persistent connections for you. It handles the connection lifecycle ($connect, $disconnect) and routing messages to your backend (e.g., Lambda functions) based on routes you define. This "Serverless WebSockets" approach removes the burden of managing fleet of servers just to hold open connections.
Cost is a major factor in the decision.
- Polling (REST API): You pay per API call. If you have 10,000 users polling every 5 seconds, that's millions of requests, which can get expensive quickly ($3.50 per million requests for REST APIs).
- WebSockets: You pay for:
- Connection Minutes: $0.25 per million connection-minutes.
- Messages: $1.00 per billion messages (first billion).
Verdict: For high-frequency updates or idle connections waiting for rare events, WebSockets are often significantly cheaper. For very infrequent checks (e.g., once an hour), polling might be cost-effective.
<h2 id="when-to-use-which">When to Use Which?</h2>| Feature | Polling (REST) | WebSockets |
|---|---|---|
| Real-time requirement | Low (seconds/minutes delay) | High (milliseconds) |
| Direction | Client-pull only | Bi-directional (Server-push) |
| Complexity | Low | Medium |
| Use Case | Weather apps, non-critical dashboards | Chat apps, stock tickers, gaming, collab tools |
Setting up a WebSocket API in AWS API Gateway involves:
- Create API: Choose "WebSocket API" in the API Gateway console.
- Define Routes:
$connect: Triggered when a client connects. Useful for auth (Lambda Authorizer).$disconnect: Triggered on disconnection.$default: Catch-all for undefined routes.- Custom routes (e.g.,
sendMessage).
- Integrate with Lambda: Connect these routes to AWS Lambda functions.
Example sendMessage Lambda (Python):
import json
import boto3
apigw_management = boto3.client('apigatewaymanagementapi', endpoint_url='https://xyz.execute-api.us-east-1.amazonaws.com/production')
def lambda_handler(event, context):
connection_id = event['requestContext']['connectionId']
body = json.loads(event['body'])
message = body['message']
# Echo message back to client
apigw_management.post_to_connection(
ConnectionId=connection_id,
Data=json.dumps({'response': f'You said: {message}'})
)
return {'statusCode': 200}
Choosing between Polling and WebSockets depends on your specific needs for latency, cost, and complexity. For true real-time interactivity, WebSockets on API Gateway provide a robust, serverless solution that scales automatically. For simpler, less time-sensitive data retrieval, Polling remains a valid and easy-to-implement strategy.
<h2 id="faq">FAQ</h2>Q: Can I use WebSockets with AWS Lambda? A: Yes, API Gateway handles the connection and invokes Lambda functions only when messages are sent or received, making it a truly serverless architecture.
Q: Is Long Polling supported by API Gateway? A: API Gateway has a 29-second timeout for integration requests. While "longish" polling is possible within this limit, true long polling usually requires longer timeouts or a dedicated backend service.
Q: Which is cheaper for 1000 users? A: It depends on the message frequency. If users are active and sending messages often, WebSockets are usually cheaper. If they are idle but just need to be "connected", WebSockets connection charges are very low compared to constant polling requests.
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External Links:
<p>Kaynak / Source: <a href="https://awsfundamentals.com/blog/polling-vs-websockets-with-amazon-api-gateway" target="_blank" rel="noopener noreferrer">https://awsfundamentals.com/blog/polling-vs-websockets-with-amazon-api-gateway</a></p>