Service Unavailable

5xx Server Error

RFC 9110

What it means

The server is temporarily unable to handle the request — either overloaded or down for maintenance. The Retry-After header may indicate when the service will be available.

Common causes

Server overloaded with traffic
Planned maintenance window
Deployment in progress
Database connection pool exhausted

How to fix it

Wait and retry. Check Retry-After header. Set up proper health checks and auto-scaling to prevent recurrence. Show a maintenance page instead of a raw 503.

Example response

HTTP/1.1 503 Service Unavailable
Retry-After: 120

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Related status codes

502Bad Gateway 504Gateway Timeout 429Too Many Requests

Other 5xx Server Error codes

500Internal Server Error 501Not Implemented 502Bad Gateway 504Gateway Timeout 505HTTP Version Not Supported 506Variant Also Negotiates

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