08Design rate limiting for a public API: what algorithm, where does it live, and what happens when the limiter itself fails?▼hard★ EssentialNewStripeCloudflareDatadogunlockedEveryone names token bucket. The scored part is the rest: drift between nodes, the 429 contract with clients, and whether your quota service should fail open or closed.Open full answer →
12A payment request times out at the gateway, so the client retries. Design the API so money moves exactly once.▼hard★ EssentialNewStripeJPMorgan ChaseGoldman Sachs○ sign inTimeouts guarantee uncertainty, not failure: the first request may have succeeded after the client gave up. The idempotency key pattern is the industry answer; the scored details are storage, expiry and concurrency.Open full answer →
13Design a URL shortener like bit.ly. What breaks first once the toy version works?▼medium★ EssentialNewAmazon & AWSFlipkartMicrosoft○ sign inThe most rehearsed design question, which is exactly why interviewers score the parts blog posts skip: redirect semantics, key generation under failure, and analytics kept off the hot path.Open full answer →
