System design · worked examples and design briefs
These are original practice prompts chosen to exercise the concepts. They are not a ranked list of current company questions. Reported question families and their evidence limits are in research.
A 45-minute practice structure
| Minutes | Produce | Check before moving on |
|---|---|---|
| 0–5 | Users, top two use cases, non-goals | Are you solving the asked product? |
| 5–10 | Scale, latency, durability, consistency | Which numbers change a decision? |
| 10–18 | API, data ownership, minimal end-to-end flow | Can one real request succeed? |
| 18–32 | One or two deep dives | Which bottleneck or failure matters most? |
| 32–40 | Recovery, operations, security, cost | What happens when a dependency is slow? |
| 40–45 | Tradeoffs and next experiment | What uncertainty would you resolve first? |
This is a practice timebox; follow an interviewer's direction. In low-level design, leave enough time for classes and executable methods. Do not spend the whole round on high-level architecture when implementation was requested.
1 · Bookmark service
Build a private bookmark API with ownership and version checks — opening contract, baseline, worked approach, changing assumptions, and assessment.
2 · Notification platform
Deliver notifications with preferences and priority — opening contract, baseline, worked approach, changing assumptions, and assessment.
3 · File synchronization
Synchronize files with resumable uploads and conflicts — opening contract, baseline, worked approach, changing assumptions, and assessment.
4 · Multi-tenant migration
Migrate tenant data with a resumable backfill — opening contract, baseline, worked approach, changing assumptions, and assessment.
5 · AI support assistant
Draft support replies without granting tool authority — opening contract, baseline, worked approach, changing assumptions, and assessment.
Explain alternatives sympathetically
For each design, defend one alternative before deciding: synchronous versus queued, SQL versus key-value, strong versus eventual reads, regional versus multi-region. State the constraint that changes your answer.
Concepts · AWS implementation · Practice rubric
Focused briefs by prerequisite
Use the owning chapter first, then state the contract, trace the baseline visual, and work through the failure and follow-ups. Constructed workload numbers are practice assumptions, not company production measurements.
Security
- Record permission changes with durable audit evidence
- Enforce tenant access in APIs, caches and exports
System design
- Build versioned API routing and admission policies
- Enforce API quotas across concurrent gateways
- Reserve rooms and handle recurring local times
- Build checkout that recovers from uncertain payments
- Build a versioned shared document editor
- Build restaurant discovery and authoritative checkout
- Collect news feeds with freshness and deduplication
- Run programming submissions inside isolated workers
- Build chat with durable messages and reconnect recovery
- Assign drivers safely with expiring offers
- Build a following feed with current access checks
- Reserve concert seats with expiring holds
- Build short links with unique aliases and safe redirects
- Process uploads and publish complete video renditions
- Build resumable uploads and authorized video playback
- Deliver signed webhooks with retries and replay
CI/CD and progressive delivery
Observability
Reliability and incident response
Data at scale
- Aggregate click events with late arrivals and reconciliation
- Protect a database with versioned cache fills
- Implement replicated writes and fenced leadership
- Search documents without leaking revoked content
- Ingest events with durable acceptance and replay
- Compute trending topics from duplicate and late events
- Build typeahead with stale-response protection
- Build a durable crawler with per-host limits
Performance and cost
AI systems
- Build a document assistant with current permissions
- Serve recommendations with safe fallback ranking