Webhooks vs Long Polling
Webhooks and long polling are two different approaches for enabling real-time data transfer and communication between servers and clients or between different services. Understanding their differences is essential for selecting the right approach for specific use cases in web development and system integration.
Webhooks vs long polling at a glance
Webhooks push: the server that owns the event sends an HTTP POST to a URL you registered the moment the event happens. Long polling pulls: your client holds a request open until the server has something to return, then immediately opens another. The table covers the differences that usually decide between them.
| Webhooks | Long polling | |
|---|---|---|
| Who starts the exchange | The server with the event, by calling your URL | The client, with a request the server holds open |
| What the receiver needs | A public HTTPS endpoint that accepts POSTs | Nothing public; any client that can make HTTP requests, including browsers and mobile apps |
| Idle cost | None; no request exists until an event occurs | One open connection per client, reopened after every response or timeout |
| When the receiver is unavailable | A well-built sender retries on a backoff schedule; delivery is at-least-once, so handlers must be idempotent | Nothing is lost server-side; the client catches up on its next request |
| Typical use | Server-to-server integrations: payment events, CI triggers, SaaS notifications | Browser and mobile clients behind NAT or firewalls that cannot expose an endpoint |
If the consumer can expose an endpoint, webhooks beat polling in general. If it cannot, compare long polling with WebSockets and with short polling before choosing.
Webhooks
Overview
- Webhooks are user-defined HTTP callbacks, which are triggered by specific events in a server or service.
- When the event occurs, the server makes an HTTP request to the URL configured for the webhook.
Key Features
- Event-Driven: Activated by specific events in the server/service.
- Server-to-Server Communication: Direct communication from the source server to the receiving server.
- Immediate Notification: Provides real-time updates as events occur.
Use Cases
- Automated Tasks: Triggering automated workflows in response to events.
- Integrations Between Services: Notifying external services of events (e.g., GitHub commits triggering CI/CD pipelines).
- Alerts and Notifications: Sending real-time alerts based on specific triggers.
Long Polling
Overview
- Long Polling is a technique where the client sends a request to the server, which holds the request open until new data is available.
- Once data is available, or a timeout occurs, the server responds and the client immediately sends a new request.
Key Features
- Client-Initiated Requests: The client initiates and maintains the request cycle.
- Reduced Latency for Client Updates: Delivers updates to the client with minimal delay.
- HTTP-Based: Uses standard HTTP protocols for communication.
Use Cases
- Chat Applications: Useful for real-time messaging applications with less frequent updates.
- Live Event Updates: For events with less frequent but real-time updates.
- Notification Systems: In systems where external event triggers are not feasible.
Key Differences
- Initiation of Communication: Webhooks are server-initiated, while long polling is initiated by the client.
- Real-Time Updates: Both provide real-time updates, but webhooks do so as a response to specific events, and long polling does it based on client requests.
- Architecture: Webhooks are ideal for server-to-server communication, whereas long polling is used for client-server communication.
- Use Case Applicability: Webhooks are suited for event-driven applications, while long polling is used when the client requires regular updates.
- Implementation Complexity: Webhooks require event handling and configuration on the server, while long polling requires keeping HTTP connections open and managing them efficiently.
The choice between webhooks and long polling depends on the specific requirements of the application, particularly the direction of data flow (server-to-server vs client-server) and the nature of the data transfer (event-driven vs continuous).