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Definition
A 502 proxy error is an HTTP status code indicating that a proxy or gateway server received an invalid or no response from an upstream server. It means the intermediary server could not successfully forward the request or return a valid response.

Why it matters
502 proxy errors disrupt website or application availability and often point to server overload, misconfiguration, network failures, or backend service outages. Persistent errors may indicate infrastructure instability or scaling issues.

Example use case
A user attempts to access a web application routed through a reverse proxy, but the backend server fails to respond properly. The proxy returns a 502 error to the user’s browser.