How do you design reliable, secure webhooks for event delivery?
⚡ Short Answer
Deliver events via signed POSTs (HMAC signature header) so receivers can verify authenticity. Use at-least-once delivery with retries + exponential backoff, include a unique event id so receivers dedupe (idempotent processing), and provide a way to replay missed events. Return 2xx fast; process async.
☕Coffee Chat Question
Concept Made Simple
“How do you design reliable, secure webhooks for event delivery?”
🧠Mind Map Answer
Remember It Faster
🔥What If?
Think Beyond the Expected
Why must a webhook receiver be idempotent even if the sender 'tries once'?
Networks make exactly-once impossible: a receiver might process an event, then its 2xx ack is lost, so the sender retries and delivers the same event again. The receiver must dedupe on the event id and process idempotently — otherwise retries cause duplicate side effects (double order, double email).
😂Real World
Stripe/GitHub webhooks sign payloads (HMAC), retry with backoff, and send a unique event id precisely so consumers can verify and dedupe; consumers that aren't idempotent get duplicate-processing bugs.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Unsigned webhooks (spoofable)
- ✗Non-idempotent receivers (duplicate side effects)
- ✗Doing heavy work before acking (timeouts → retries)
✅Best Practices
- ✓Sign payloads (HMAC) and verify on receipt
- ✓Ack 2xx fast; process async; dedupe by event id
- ✓Retry with backoff; offer replay
🔁Follow-up Questions
- 1How does HMAC signature verification work?
- 2Why ack quickly and process asynchronously?
- 3How do you let consumers replay missed events?
🧩Related Technologies
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Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: Idempotency (REST APIs) Interview question: "How do you design reliable, secure webhooks for event delivery?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
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