Interview Q&A / System Design
System Design interview questions
Caching, scaling, databases and classic design problems for beginners.
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- Which HTTP methods are safe and which are idempotent?
Safe methods (GET, HEAD, OPTIONS) don't change server state. Idempotent methods (GET, PUT, DELETE and the safe ones) give the same result when repeated. POST is neither, and PATCH is not guaranteed idempotent.
BeginnerQuick answer1 min read - Which HTTP status codes should every API developer know?
Know the families: 2xx success (200, 201, 204), 3xx redirect (301, 304), 4xx client error (400, 401, 403, 404, 409, 429), 5xx server error (500, 502, 503, 504). The code tells clients whether retrying can help.
BeginnerQuick answer1 min read - How do Cache-Control and ETag headers work together?
Cache-Control says how long a response may be reused without asking. ETag is a fingerprint of the content; after expiry the browser sends it back, and the server replies 304 Not Modified if nothing changed, saving the download.
IntermediateQuick answer1 min read