Design a notification system

Q: Design a notification system

This question evaluates a candidate's competency in designing scalable, reliable multi-channel notification platforms, covering distributed systems, multitenancy, API and storage schema design, queuing and retry strategies, rate limiting, observability, localization, A/B testing, and compliance considerations like GDPR.

Q: 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.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at DoorDash.

Q: What role is this question designed for?

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

Question

System Design: Multi-Channel Notification Platform

Context

Design a multi-tenant notification platform that delivers messages across email, SMS, and mobile push. The system must support both real-time and scheduled notifications, per-user preferences, and be resilient, scalable, and cost-aware.

Functional Requirements

Channels: email, SMS, push notifications.
Delivery modes: real-time and scheduled (one-time and recurring).
User controls: per-user preferences (opt-in/out per category), quiet hours, locale/time zone.
Reliability: deduplication, idempotency, retries with exponential backoff.
Throttling: rate limiting per user, per tenant, and per provider.
Isolation: strict multi-tenant isolation (configs, limits, data segregation).
Content: templating with variables, localization (i18n, l10n), and A/B testing support.
Observability: monitoring, alerting, delivery analytics.
Compliance: GDPR/data minimization, consent management, auditability.
Cost controls: budgets/quotas and provider selection for cost/performance.

Non-Functional Requirements

High availability; horizontal scalability.
Message delivery latency targets and throughput (TPS) goals.
Delivery semantics: discuss exactly-once vs at-least-once.
Graceful degradation and failure-mode strategies.

Deliverables

Public APIs (send, schedule, templates, preferences, status).
Storage schema (entities, key indexes, partitioning).
Queue/pub-sub design and retry strategy.
Worker orchestration and provider integration patterns.
Monitoring/alerting and analytics plan.
Scalability targets (e.g., p99 latency, TPS) with reasoning.
Failure modes and mitigations.
A/B testing strategy.
GDPR/compliance approach.
Cost controls and budgets.

Design a notification system

Quick Overview

Design a notification system

System Design: Multi-Channel Notification Platform

Context

Functional Requirements

Non-Functional Requirements

Deliverables

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