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503
Server Error

HTTP status code 503 Service Unavailable

HTTP 503 Service Unavailable is the status code for a temporary outage: the server is overloaded or down for maintenance and asks clients to come back later, optionally with a Retry-After header.

Fixing this error on a site, a server or an API? Step-by-step guide: 503 Service Unavailable: Meaning (RFC 9110) and Fixes →

Definition (RFC 9110)

HTTP status code 503 Service Unavailable is defined in RFC 9110 (HTTP Semantics), Section 15.6.4 — the current authoritative specification for HTTP semantics, published June 2022, which obsoletes the older RFC 7231 and RFC 2616.

Description

The 503 Service Unavailable status code indicates that the server is currently unable to handle the request due to temporary overload or scheduled maintenance. The response may include a Retry-After header indicating when the service is expected to be available.

Common Causes

  • Server maintenance
  • Server overload
  • Application deployment in progress
  • Rate limiting at infrastructure level
  • Resource exhaustion (CPU, memory, connections)

How to Fix

  • Wait and retry the request
  • Check server status page
  • Scale server resources
  • Implement graceful degradation
  • Set up load balancing

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Related Status Codes

500
500 Internal Server Error
HTTP 500 Internal Server Error is the generic status code a server returns when a failure on its own side, such as an application exception or a broken configuration, stops it from completing a request. The cause is in the server logs, not in the request.
 501
501 Not Implemented
The server does not support the functionality required to fulfill the request.
 502
502 Bad Gateway
HTTP 502 Bad Gateway is the status code a proxy, load balancer or CDN returns when the upstream server behind it refused the connection or sent a response it could not use.
 504
504 Gateway Timeout
HTTP 504 Gateway Timeout is the status code a proxy, load balancer or CDN returns when the upstream server behind it did not answer in time.
 505
505 HTTP Version Not Supported
The server does not support the HTTP protocol version used in the request.
 507
507 Insufficient Storage
The server cannot store the representation needed to complete the request (WebDAV).

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