Start by clarifying requirements (scale, latency, ordering guarantees, delivery semantics) and then walk through the end-to-end flow: event ingestion, durable queueing, delivery workers with retries and backoff, and dead-letter handling. Emphasize trade-offs (e.g., ordering vs throughput, at-least-once vs exactly-once) and how you'd monitor and scale the system.
Pro tip: Proactively discuss idempotency and how clients can deduplicate events, since webhook delivery is typically at-least-once; this shows you understand real-world reliability constraints. Also, mention that you'd provide a way for clients to verify webhook authenticity (e.g., HMAC signatures) and handle replay attacks.
Ask about expected event volume, latency requirements, ordering needs, and delivery guarantees (at-least-once vs exactly-once). This shapes the entire design.
Describe how events enter the system (API, internal producers) and are durably queued (e.g., Kafka, SQS) with partitioning for scale and ordering.
Explain how workers consume events, attempt HTTP POST with timeouts, and retry with exponential backoff and jitter. Include idempotency keys and authentication (e.g., HMAC signatures).
After max retries, move events to a DLQ for manual inspection or alerting. Discuss how to replay DLQ events and avoid poison messages.
Scale workers horizontally, monitor queue depth, delivery latency, success rates, and set up alerts. Discuss ordering vs throughput (e.g., per-endpoint ordering with partitioned queues) and other trade-offs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.