1.3.1. The Response line



Line 1 is the “response line”. It is always composed of 3 fields :

  • a version tag : HTTP/1.1
  • a status code : 200
  • a reason : OK

The status code is always 3-digit. The first digit indicates a general status :

  • 1xx = informational message to be skipped (eg: 100, 101)
  • 2xx = OK, content is following (eg: 200, 206)
  • 3xx = OK, no content following (eg: 302, 304)
  • 4xx = error caused by the client (eg: 401, 403, 404)
  • 5xx = error caused by the server (eg: 500, 502, 503)

Please refer to RFC2616 for the detailed meaning of all such codes. The “reason” field is just a hint, but is not parsed by clients. Anything can be found there, but it’s a common practice to respect the well-established messages. It can be composed of one or multiple words, such as “OK”, “Found”, or “Authentication Required”.

Haproxy may emit the following status codes by itself :

Code When / reason
200 access to stats page, and when replying to monitoring requests
301 when performing a redirection, depending on the configured code
302 when performing a redirection, depending on the configured code
303 when performing a redirection, depending on the configured code
307 when performing a redirection, depending on the configured code
308 when performing a redirection, depending on the configured code
400 for an invalid or too large request
401 when an authentication is required to perform the action (when accessing the stats page)
403 when a request is forbidden by a "block" ACL or "reqdeny" filter
408 when the request timeout strikes before the request is complete
500 when haproxy encounters an unrecoverable internal error, such as a memory allocation failure, which should never happen
502 when the server returns an empty, invalid or incomplete response, or when an "rspdeny" filter blocks the response.
503 when no server was available to handle the request, or in response to monitoring requests which match the "monitor fail" condition
504 when the response timeout strikes before the server responds

The error 4xx and 5xx codes above may be customized (see “errorloc” in section 4.2).

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