URL shortener
Warm-up · 1,000,000 req/s
A read-heavy redirect service (99% reads). Short codes are hot and cacheable; writes create new links.
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System design interview scenarios
9 classic system design problems, from warm-up to advanced. Each one starts with an architecture that breaks under load and a pass/fail goal. Scale it, add caches, queues and replicas, and watch the simulation tell you whether it holds.
Video streaming CDN
Warm-up · 2,000,000 req/s
Two million segment requests per second, almost all reads, served from a distant origin whose latency varies a lot.
News feed
Intermediate · 200,000 req/s
A social feed under a daily traffic wave. Feeds are assembled from a timeline cache, with a slow ranking API on the critical path.
Chat system
Intermediate · 200,000 req/s
Half the traffic sends messages, half fetches recent history. One database takes both, and writes alone exceed what a single primary can do.
Search typeahead
Intermediate · 500,000 req/s
Suggestions must appear while the user types: a tight p99 at half a million lookups per second, against an index with long-tail latency.
Ticket flash sale
Intermediate · 300,000 req/s
Tickets go on sale and traffic spikes 10x in seconds. Most requests try to reserve a seat (writes), all hitting one primary database.
API rate limiting
Intermediate · 100,000 req/s
A burst of client traffic pushes the API past capacity. Queues grow, requests time out, clients retry, and the whole API collapses even though it is only ~10% short.
Payment processing
Advanced · 5,000 req/s
Every request goes to a slow third-party payment provider, including status checks that could be answered locally. The provider limits concurrent calls, and aggressive retries turn every slowdown into an outage.
Multi-region failover
Advanced · 300,000 req/s
Two regions share the load behind a global load balancer. At t = 15 s, us-east goes dark for 20 s. Health checks move its traffic to us-west, and us-west has to survive the double load.