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529 Site Is Overloaded

Non-standard code used by a few platforms to indicate the site is overloaded and shedding requests.

Status

HTTP/1.1 529 Site Is Overloaded

Details

  • Category: 5xx
  • Status: Unofficial (Qualys and other vendors). Not registered with IANA. A server, framework, or CDN convention.
  • Specification: none, not defined by any RFC
  • Cacheable: Not cacheable
  • Response body: Allowed
  • Retry: Retry after a delay

529 is used by a small number of vendors, notably Qualys SSLLabs, to signal that the service is too busy to accept the request. It is not registered and has no standard meaning.

Treat it exactly as you would a 503: back off and come back later.

Common causes

  • A service deliberately shedding load during a traffic spike.

How to fix it

As the client

  • Back off with jitter and retry later. Queue the work rather than hammering the endpoint.

As the server

  • Return 503 with Retry-After so standard clients handle the condition correctly.

Examples

A service shedding load

HTTP request

GET /api/analyze?host=example.com HTTP/1.1
Host: api.ssllabs.com

HTTP response

HTTP/1.1 529 Site is overloaded

See also