Design notification and project architecture

Q: Design notification and project architecture

This question evaluates a candidate's ability to design scalable, resilient multi-channel notification platforms, testing skills in distributed systems, messaging and queuing, data modeling for templates and schedules, API design, observability, and operational concerns such as retries, provider failover, idempotency, and regulatory compliance.

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Question

System Design: Multi-Channel Notification Platform

Design a scalable Notification System that supports real-time and scheduled messages across multiple channels (email, push, SMS). Assume this is for a high-traffic consumer platform with millions of users and mission-critical notifications.

Assumptions (you may adjust if you state them explicitly):

Traffic: up to 50k notifications/second at peak, 1B/day worst case during major events.
Channels: email, mobile push, SMS; multiple third-party providers per channel for redundancy.
Scheduling: immediate and future delivery (seconds to 30 days ahead), with cancel/reschedule.
Global audience with time zones, quiet hours, user preferences, and regulatory constraints.

Deliverables

Components: Enumerate core services and infra.
Data flow: Real-time and scheduled paths end-to-end.
Storage: Schemas/data models for templates, preferences, schedules, logs, idempotency.
Failure handling: Retries, deduplication, provider failover, DLQs, backpressure.
Scaling strategy: Partitioning, autoscaling, rate limiting, multi-region.

Also provide:

APIs: send now, schedule, cancel, update preferences, provider callbacks.
Observability: metrics, tracing, alerting, and SLOs.
Capacity planning example.
Security and compliance considerations.

Project Architecture Walkthrough (Past Project)

Pick one substantial system you have built or owned. Draw and explain the end-to-end architecture:

Services and their responsibilities.
Databases/storage choices and schemas.
Communication patterns (sync vs async, queues, streams, webhooks), data consistency strategy (e.g., outbox/Saga).
Scaling, availability, and failure modes.
Tradeoffs and lessons learned.

Be prepared for deep, domain-specific follow-ups (e.g., exact-once semantics, time-zone correctness, multi-tenant throttling, provider outage strategy, replay/backfill, GDPR deletion).

Design notification and project architecture

System Design: Multi-Channel Notification Platform

Project Architecture Walkthrough (Past Project)

Solution

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