Popular System Design Topic

The system-design questions worth practicing, grouped into patterns so no shape catches you cold. For the vocabulary that comes up along the way, see Terminology.

Question patterns to cover

Like coding interviews, system design questions cluster into patterns. Practice at least one from each category so no shape catches you cold:

Pattern	Representative system	Core challenge
Online ticketing	Ticketmaster	Consistency & concurrency under high-demand sales
Streaming / content delivery	YouTube, Netflix	Real-time streaming, CDN, large blobs
Location-based	Uber, Yelp	Geo indexing, location tracking, proximity search
E-commerce	Amazon	Scalability + transaction management
Social network	Twitter, FB News Feed, Instagram	Data scale, real-time updates, fan-out
Messaging	WhatsApp, FB Live Comments	Real-time delivery, presence, notifications
Banking / financial	Robinhood, payment system	Security, privacy, transaction consistency
Collaborative editing	Google Docs	Concurrency & conflict resolution (CRDT/OT)
Cloud storage	Dropbox	Efficient, scalable file storage & sharing
Competition / leaderboards	LeetCode, top-K	Real-time interaction, ranking at scale
URL shortener / ID generation	Bitly, TinyURL, Snowflake	Read-heavy lookups, short-key generation, no collisions
Search / autocomplete	Typeahead, FB post search	Inverted index, prefix matching, ranking at scale
Analytics / stream aggregation	Ad-click aggregator, metrics monitoring	High-volume ingest, windowed aggregation, approximate top-K
Notifications	Push / email / SMS	Multi-channel fan-out, dedup, delivery guarantees
Foundational component	Rate limiter, message queue, distributed cache, web crawler, job scheduler	One building block, deeply

Advanced / infra deep dives

Beyond the common pool — infrastructure-flavored, often staff-level. Not what you’d be handed in a typical product-design round, but high-value if you work on platforms or interview for infra roles. Several lean on the same internals as the Postgres Internals page.

Problem	Angle	What it drills
Payments API layer	Stripe	Idempotency keys, exactly-once charges, API versioning, webhook delivery
Durable execution engine	Temporal, from scratch	Persisting workflow state, deterministic replay, timers, retries at scale
Multi-tenant search service	Per-tenant SaaS search	Tenant isolation + relevance with no per-customer code
Managed database service (DBaaS)	RDS / Aurora	Fleet provisioning, multi-tenant ops, control plane vs. data plane
HA & automated failover	Replica promotion	Leader election, split-brain avoidance, RTO/RPO targets
Zero-downtime upgrades	Rolling version changes	Connection draining, backward-compatible schemas, online migrations
Backup & restore with PITR	Continuous WAL archiving	Point-in-time recovery, restore SLAs, WAL-based replay
Control plane / data plane isolation	Any managed service	Keeping management-layer failures off the serving path