How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

What difficulty level is this interview question?

This is a medium difficulty System Design question, commonly asked during Onsite rounds at Airbnb.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Airbnb during technical interviews.

Design a scalable notification system | Airbnb Interview Question

Quick Overview

This question evaluates expertise in large-scale system design and distributed messaging, assessing competencies in event-driven and batch processing, multi-channel delivery, message templating and personalization, user preference and compliance handling, reliability concerns like retries and deduplication, scalability strategies, and observability. It is commonly asked to probe architectural reasoning about throughput, fault tolerance, backpressure, rate limiting, routing and trade-offs between real-time versus bulk delivery, and it falls under the System Design and distributed systems/messaging domain with emphasis on practical application of high-level architectural patterns rather than low-level implementation details.

Problem

Design a notification system for a company at Airbnb-like scale that can send notifications to different user types (e.g., customers/guests, hosts, employees) through multiple delivery channels:

Email
SMS
Push notifications
Social/Tweet-like channel (optional integration)

The system must support two delivery modes:

Single / Event-triggered notifications : triggered by a real-time event (e.g., booking confirmed → email to guest; check-in day → SMS with lock code).
Bulk / Batch notifications : triggered by a scheduled or ad-hoc campaign to a target group (e.g., promotional content to potential hosts).

Expectations

Describe an end-to-end design that covers:

Core components and data flow for both event-triggered and batch sends
How messages are authored (templates), personalized, and routed to channels
User preferences (opt-in/out), frequency limits, and compliance (unsubscribe)
Reliability: retries, deduplication, ordering (if needed), idempotency
Scalability: high throughput, fan-out, backpressure, and rate limiting
Observability: logging, metrics, tracing, and auditing

You may assume existing product services emit events (booking, check-in, campaign creation, etc.) and your system consumes them to deliver notifications.

Design a scalable notification system

Quick Overview

Problem

Expectations

Solution

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