HTTP 503 Service Unavailable

What this status code means

Service Unavailable describes how the server processed the request and what the client should do next.

Who should act first

Service, gateway, or upstream dependency is usually the first place to investigate.

What to check first

• Correlate request ID across edge, proxy, and app logs.
• Check upstream dependency health and timeouts.
• Review recent deploy or config changes.

How it differs from similar codes

• HTTP 502 Bad Gateway — full guide
• HTTP 504 Gateway Timeout — full guide

Reference and next step

Specification: RFC 9110.

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