Failure Training
The interview question that separates seniors: 'what happens if this fails?' Step through each cascade one failure at a time, then reveal how real systems contain the blast radius.
Caching
A hot cache key expires under load
Trigger
A popular key (e.g. the homepage feed) expires while receiving 50k req/s.
The cascade
- 1Every request misses the cache simultaneously
- 2All of them hit the database at once (thundering herd)
- 3DB connection pool saturates, queries queue up
- 4Latency spikes → upstream timeouts → retries → more load
- 5Database falls over, cascading to every dependent service
Step 1 of 5
Blast radius
Entire read path for anything backed by that database.