Systems integrate through two primary patterns for receiving updates: webhooks and polling. Webhooks push notifications immediately when events occur. Polling periodically checks for changes. Each approach has distinct advantages and challenges. Webhooks provide real-time updates but require publicly accessible endpoints. Polling offers simplicity but wastes resources checking for changes that rarely occur.
Choosing between webhooks and polling depends on requirements around latency, reliability, scale, and implementation complexity. Understanding practical tradeoffs helps teams make informed decisions.
How Webhooks Work
Webhooks deliver notifications by making HTTP requests to URLs you provide when events occur. Register webhook URLs with external services. When events happen, the service makes HTTP POST requests to your endpoints with event data. Your application receives notifications immediately without checking constantly. This event-driven approach minimizes latency between events occurring and your system knowing about them. Payment processors use webhooks to notify merchants when payments complete. Git hosting services use webhooks to trigger CI/CD pipelines when code is pushed. The push model eliminates unnecessary network requests. Your system only receives traffic when something actually happens. This scales efficiently for high-frequency events. Webhooks enable real-time responses. Order fulfillment can begin immediately when payment webhooks arrive rather than waiting for polling cycles. Webhooks require publicly accessible HTTP endpoints. Your service must accept incoming requests from external systems. This means deploying endpoints that external services can reach, configuring firewalls appropriately, and ensuring availability. Webhook handling must be fast. Services expect quick responses and may timeout or retry if your endpoint is slow. Process webhook payloads asynchronously rather than performing long operations synchronously.
How Polling Works
Polling repeatedly checks external systems for updates at regular intervals. Your application makes periodic API requests checking for new data or state changes. Poll every minute, every 5 minutes, or whatever interval makes sense. This pull model gives you complete control over when and how often you check for updates. No external services need access to your infrastructure. Polling is simple to implement. Make HTTP requests on a schedule. No special infrastructure required. Polling works behind firewalls. Your systems don’t need to be publicly accessible. You control checking frequency. Polling generates network traffic regardless of whether changes occurred. Checking every minute makes 1440 requests daily even if nothing changes. API rate limits constrain polling frequency. Polling introduces latency. Events occurring after a poll won’t be discovered until the next cycle.
Latency Comparison
Event notification latency differs significantly between approaches. Webhooks provide near-instant notification. Events trigger webhook deliveries within seconds. For time-sensitive workflows, this immediacy matters. Payment confirmations, fraud alerts, or system failures need immediate attention. Well-implemented webhooks deliver notifications in under a second. Polling latency equals your polling interval. Checking every 5 minutes means events take up to 5 minutes to discover. This is acceptable for many use cases. Synchronizing customer data overnight works fine with hourly polling. For critical real-time workflows, polling latency is problematic.
Reliability and Failure Handling
Both approaches face reliability challenges. Webhook delivery can fail for many reasons. Your endpoint is down, network issues prevent requests, or your service responds slowly. Good webhook providers retry failed deliveries with exponential backoff. You must handle duplicate deliveries since retries might succeed after initial failures. Store webhook IDs and check for duplicates. Some webhook senders don’t retry at all. Polling reliability depends on your implementation. If your polling service crashes, you miss events until it restarts. Polling can detect missed events by tracking last-checked timestamps. Many systems use both approaches for reliability. Webhooks provide real-time notifications. Periodic polling acts as backup, catching failed webhooks.
Security Considerations
Security requirements differ substantially between push and pull models. Verify webhook authenticity before processing. Attackers can send fake webhook requests. Most webhook providers sign requests using HMAC signatures in headers. Compute expected signatures using shared secrets and compare to request signatures. Reject mismatches. Webhook endpoints are publicly accessible, making them potential attack vectors. Implement rate limiting, input validation, and DDoS protection. Store webhook signing secrets securely and rotate them periodically. Polling requires API credentials giving access to external systems. Protect these credentials. Use service accounts with minimum necessary permissions. Store credentials in secret management systems. Polling originates from your infrastructure, giving you control over network paths. Polling doesn’t expose your infrastructure to inbound attacks, reducing attack surface compared to webhooks.
Scalability Patterns
Scaling challenges differ between approaches. Webhook receivers must handle traffic spikes when events surge. Flash sales or viral content can cause webhook floods. Design endpoints to queue work quickly and return responses fast. Process payloads asynchronously using job queues. Multiple instances behind load balancers distribute webhook traffic. Ensure idempotent processing since load balancing and retries can cause duplicate deliveries. Polling scales by distributing work across multiple workers. Partition polling responsibilities so different workers check different resources. Use distributed locking to prevent duplicate polling. Polling generates predictable load on external APIs. Respect rate limits to avoid bans.
Cost Implications
Each approach has different cost characteristics. Webhooks require constantly running infrastructure to receive events. Even with low event volumes, webhook endpoints must remain available. Polling only consumes resources during polling cycles. For infrequent checks, polling may be cheaper. Some APIs charge per request. Polling costs accumulate with every check regardless of results. Webhooks avoid these charges by only delivering when events occur. For high-frequency events, webhooks save significant API costs.
Development Complexity
Implementation complexity varies significantly. Webhooks require more infrastructure setup. Deploy publicly accessible endpoints, configure DNS, set up SSL certificates, and implement signature verification. Testing webhooks is harder since you need the external service to send requests. Debugging webhook issues is challenging. Problems might be on the sender’s side, in network transit, or in your handling code. Polling is conceptually simpler. Schedule periodic API calls. Compare results. Act on changes. Testing is straightforward since you control when polling occurs. Debugging polling issues is easier. The logic is deterministic and repeatable.
When to Use Webhooks
Certain scenarios strongly favor webhooks. Real-time or near-real-time responses require webhooks. Payment processing, fraud detection, and alert systems need immediate notification. Polling’s inherent delay is unacceptable. CI/CD pipelines triggering on code pushes or order fulfillment beginning on payment confirmation need webhooks. When events occur frequently, webhooks avoid polling overhead. Chat applications with constant messages or financial data feeds updating many times per second generate too much traffic for polling. API rate limits often make polling infeasible for high-frequency events.
When to Use Polling
Many situations make polling the pragmatic choice. Corporate networks or certain cloud environments restrict inbound traffic. Deploying publicly accessible webhook endpoints may be impossible or require extensive security reviews. Polling works within these constraints. Infrastructure simplicity favors polling when you can’t easily expose endpoints. Not all webhook implementations are reliable. Some services don’t retry failed deliveries. If webhook reliability is questionable, polling provides more control. Polling works when webhooks aren’t available. Many APIs don’t offer webhooks at all. When delays of minutes or hours don’t matter, polling’s simplicity wins. Nightly data synchronization, periodic report generation, or background analytics don’t need real-time updates.
Hybrid Approaches and Best Practices
Combining both patterns leverages strengths of each. Use webhooks for real-time notifications but poll periodically as backup. If webhooks fail, polling eventually catches missed events. Set polling intervals much less frequently than needed since webhooks handle normal operation. Another pattern: poll to discover new resources, then register webhooks for updates. Both webhooks and polling can cause duplicate processing. Webhooks retry failed deliveries. Polling might reprocess events if state tracking fails. Implement idempotent handlers that safely process the same event multiple times. Monitor webhook delivery success rates. Alert when failure rates exceed thresholds. For polling, monitor for missed polling cycles. Design systems to degrade gracefully when integrations fail. Queue events for later processing rather than dropping them.