System Design · Junior · Question 56 of 75

How do `502`, `503` and `504` differ?

✓Correct answer: 502: a gateway got an invalid response from upstream; 503: the service is unavailable (overload/maintenance); 504: the upstream timed out
2They all mean "page not found"
3They're client errors

Explanation

These codes help locate the problem: the proxy, the app servers or a slow dependency. 503 often comes with Retry-After.

Further reading

MDN: HTTP response status codes ↗

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