Product Changelog / Release Notes

Interview-Ready Approach

1) Clarify Scope and SLOs

• •Problem statement: Design a hosted changelog service where product teams publish release notes and users subscribe to updates.
• •Design for a peak load target around 500 RPS (including burst headroom).
• •Product teams: ~1,000
• •Entries per product/month: ~5
• •Widget impressions/month: ~500,000
• •Widget load time: < 300 ms
• •Email notification delay: < 30 minutes

2) Capacity Planning Method

• •Convert traffic and growth constraints into request rate, storage growth, and concurrency budgets.
• •Keep at least 2-3x safety margin per tier (ingress, compute, storage, async workers).
• •Reserve explicit latency budgets per hop so p95 can be defended in review.

3) Architecture Decisions

• •Databases: Define a clear system-of-record and design read/write paths separately before adding optimizations.
• •API Design: Standardize API boundaries, idempotency keys, pagination, and error contracts first.
• •CDN: Serve static and cacheable content from edge and keep origin strictly for misses and dynamic requests.

4) Reliability and Failure Strategy

• •Use strong write constraints (transactions or conditional writes) and explicit backup/restore strategy.
• •Apply strict input validation and backward-compatible versioning.
• •Define cache keys and purge workflows before launch to avoid stale/global outages.

5) Validation Plan

• •Run one peak-load test, one dependency-degradation test, and one failover test.
• •Verify idempotency for all retried writes and async consumers.
• •Track user-facing SLOs first: p95 latency, error rate, and successful throughput.

6) Trade-offs to Call Out in Interviews

• •Databases: SQL gives stronger transactional guarantees; NoSQL often gives better write scaling and flexibility.
• •API Design: Rich APIs improve developer speed but can create long-term compatibility burden.
• •CDN: Long TTL improves latency/cost; short TTL improves freshness.

Practical Notes

• •The changelog page is read-heavy and rarely changes - serve it as cached HTML from a CDN, invalidate on publish.
• •The widget is a lightweight JS script that fetches the latest 5 entries from an API endpoint. Cache aggressively.
• •Track 'last seen' timestamp per user to compute the unread badge count in the widget.

Why This Solution Works

Request path: The solution keeps ingress, service logic, and stateful dependencies separated so each layer can scale independently.

Reference flow: Web Clients -> DNS -> CDN Edge -> API Gateway -> API Service -> Primary SQL DB

Design strengths

• •The architecture keeps synchronous paths short and isolates stateful dependencies behind clear boundaries.

Interview defense

• •This design makes bottlenecks explicit (ingress, core compute, persistence, async workers).
• •It supports progressive scaling without re-architecting the core request path.
• •It keeps correctness-sensitive state changes in durable systems while offloading background work asynchronously.