What Is Event-Driven Serverless Design?

Event-driven serverless design is an architecture where lightweight functions automatically react to events (like file uploads, queue messages, or API triggers), scaling on demand and charging only when executed. (#definition)

When to Use

Applications with spiky or unpredictable traffic (e.g., user signups, uploads).
Data pipelines like ETL, log processing, and IoT telemetry.
Real-time workflows such as notifications, webhooks, or background tasks.
Fast prototyping and MVPs where quick iteration matters.

Example

When a user uploads a photo, a function triggers to generate thumbnails, store metadata, and push a message into a queue for indexing.

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Why Is It Important

Decouples services, enabling teams to work independently.
Autoscaling saves cost and simplifies operations.
Built-in reliability and retries reduce infrastructure headaches.

Interview Tips

Clearly define event, producer, consumer, and idempotency.
Mention at-least-once delivery and dead-letter queues.
Draw a simple flow of producers → queue/topic → consumers.
Highlight cost savings and resilience in your answer.

Trade-offs

Pros: Fast iteration, low ops overhead, pay-per-use, elastic scaling. Cons: Cold starts, vendor lock-in, distributed debugging, eventual consistency.