HTTP Status Codes

External

• RFC2616 http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

Internal

• HTTP Response

Overview

The status line consists of a numeric status code, followed by a space and a reason phrase string.

The first digit of the status code defines the class of response:

• 1xx: Informational
• 2xx: Success
• 3xx: Redirection
• 4xx: Client Errors
• 5xx: Server Error

An unrecognized status code must be treated as being equivalent to the x00 status code of that class

More details in RWA Appendix A - The Status Codex, page 295.

1xx Informational Status Codes

Request received, continuing process.

100 Continue

https://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.2.3

2xx Success Status Codes

The action was successfully received, understood, and accepted.

201 Created

Signifies that everything is OK and a new resource was created as response to the request. The Location header may contain the URL of the newly created resource.

204 No Content

Appropriate response to a successful DELETE request.

3xx Redirection Status Codes

This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. The action required may be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD. A client should detect infinite redirection loops, since such loops generate network traffic for each redirection.

301 Moved Permanently

The requested resource has been assigned a new permanent URI and any future references to this resource should use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.

The new permanent URI should be given by the Location field in the response. Unless the request method was HEAD, the entity of the response should contain a short hypertext note with a hyperlink to the new URI(s).

If the 301 status code is received in response to a request other than GET or HEAD, the user agent must not automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.

302 Found

Also known as "Moved Temporarily".

The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client should continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.

The temporary URI should be given by the Location field in the response. Unless the request method was HEAD, the entity of the response should contain a short hypertext note with a hyperlink to the new URI(s).

If the 302 status code is received in response to a request other than GET or HEAD, the user agent must not automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.

303 See Other

The response to the request can be found under a different URI and should be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response must not be cached, but the response to the second (redirected) request might be cacheable.

The different URI should be given by the Location field in the response. Unless the request method was HEAD, the entity of the response should contain a short hypertext note with a hyperlink to the new URI(s).

304 Not Modified

If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server should respond with this status code. The 304 response must not contain a message-body, and thus is always terminated by the first empty line after the header fields.

The response must include the following header fields:

• Date, unless its omission is required by section 14.18.1 in RFC 2616.
• ETag and/or Content-Location, if the header would have been sent in a 200 response to the same request
• Expires, Cache-Control, and/or Vary, if the field-value might differ from that sent in any previous response for the same variant.

If the conditional GET used a strong cache validator (see section 13.3.3), the response should not include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response most not include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. If a 304 response indicates an entity not currently cached, then the cache must disregard the response and repeat the request without the conditional. If a cache uses a received 304 response to update a cache entry, the cache must update the entry to reflect any new field values given in the response.

305 Use Proxy

The requested resource mustbe accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses must only be generated by origin servers.

306 (Unused)

The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.

307 Temporary Redirect

The requested resource resides temporarily under a different URI. Since the redirection may be altered on occasion, the client should continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.

The temporary URI should be given by the Location field in the response. Unless the request method was HEAD, the entity of the response should contain a short hypertext note with a hyperlink to the new URI(s) , since many pre-HTTP/1.1 user agents do not understand the 307 status. Therefore, the note should contain the information necessary for a user to repeat the original request on the new URI.

If the 307 status code is received in response to a request other than GET or HEAD, the user agent must not automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.

4xx Client Errors

The request contains bad syntax or cannot be fulfilled. A 4xx response code is indicative of a client error.

400 Bad Request

The request could not be understood by the server due to malformed syntax. The client should not repeat the request without modifications, it should attempt to fix the request first.

401 Unauthorized

The server understood the request but it refuses to take further action because request requires user authentication.

The server response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. The client may repeat the request with a suitable Authorization header field.

If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials.

If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user should be presented the entity that was given in the response, since that entity might include relevant diagnostic information.

For more on HTTP basic authentication, see https://home.feodorov.com:9443/wiki/Wiki.jsp?page=HTTPBasicAuthentication.

403 Forbidden

The server understood the request, but is refusing to fulfill it, possibly because it is configured to deny access for some reason to the requested resource.

Authorization will not help and the request should not be repeated.

If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it should describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not Found) can be used instead.

404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

The 410 (Gone) status code should be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.

Exchange Example

GET /blah HTTP/1.1
Host: localhost
User-Agent: curl/7.43.0
Accept: */*

HTTP/1.1 404 Not Found
Date: Fri, 06 Jan 2017 19:07:37 GMT
Server: Apache/2.2.26 (Unix)
Content-Length: 202
Content-Type: text/html; charset=iso-8859-1

<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>404 Not Found</title>
</head><body>
<h1>Not Found</h1>
<p>The requested URL /blah was not found on this server.</p>
</body></html>

405 Method Not Allowed

The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response must include an Allow header containing a list of valid methods for the requested resource.

Kubernetes documentation: The action attempted by the client is not supported by the code.

406 Not Acceptable

The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.

Unless it was a HEAD request, the response should include an entity containing a list of available entity characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice may be performed automatically. However, this specification does not define any standard for such automatic selection.

Note that HTTP/1.1 servers are allowed to return responses which are not acceptable according to the accept headers sent in the request. In some cases, this may even be preferable to sending a 406 response. User agents are encouraged to inspect the headers of an incoming response to determine if it is acceptable. If the response could be unacceptable, a user agent should temporarily stop receipt of more data and query the user for a decision on further actions.

407 Proxy Authentication Required

This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy must return a Proxy-Authenticate header field containing a challenge applicable to the proxy for the requested resource. The client may repeat the request with a suitable Proxy-Authorization header field.

408 Request Timeout

The client did not produce a request within the time that the server was prepared to wait. The client may repeat the request without modifications at any later time.

409 Conflict

The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body should include enough information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.

Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.

Other Situations

409 was triggered while attempting to create (POST) a resource that already exists.

410 Gone

The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent. Clients with link editing capabilities should delete references to the Request-URI after user approval. If the server does not know, or has no facility to determine, whether or not the condition is permanent, the status code 404 (Not Found) should be used instead. This response is cacheable unless indicated otherwise.

The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time. That is left to the discretion of the server owner.

411 Length Required

The server refuses to accept the request without a defined Content- Length. The client may repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request message.

412 Precondition Failed

The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.

413 Request Entity Too Large

The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server may close the connection to prevent the client from continuing the request.

If the condition is temporary, the server should include a Retry- After header field to indicate that it is temporary and after what time the client may try again.

414 Request-URI Too Long

The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some servers using fixed-length buffers for reading or manipulating the Request-URI.

415 Unsupported Media Type

The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.

416 Requested Range Not Satisfiable

A server should return a response with this status code if a request included a Range request-header field, and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field. (For byte-ranges, this means that the first- byte-pos of all of the byte-range-spec values were greater than the current length of the selected resource.)

When this status code is returned for a byte-range request, the response should include a Content-Range entity-header field specifying the current length of the selected resource. This response must not use the multipart/byteranges content- type.

417 Expectation Failed

The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.

4xx Errors Not Specified by the Standard

422 Unprocessable Entity

Generated by Kubernetes APIs. Indicates that the requested create or update operation cannot be completed due to invalid data provided as part of the request.

429 Too Many Requests

Generated by Kubernetes APIs. Indicates that the either the client rate limit has been exceeded or the server has received more requests then it can process.

5xx Server Errors

The server failed to fulfill an apparently valid request.

500 Internal Server Error

The server encountered an unexpected condition which prevented it from fulfilling the request.

502 Bad Gateway

The server, while acting as a proxy, received an invalid response from the backend server. This is sometimes reported as 502 Proxy Error.

This status code is returned by a httpd proxy if the answer from the backend server does not arrive in the configured timeout.

503 Service Unavailable

The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay MAY be indicated in a Retry-After header. If no Retry-After is given, the client SHOULD handle the response as it would for a 500 response.

Cases when httpd returns 503:

• No backend nodes are available to proxy a mod_proxy load balanced request.

504 Gateway Timeout

The 504 Gateway Timeout error is an HTTP status code that means that one server did not receive a timely response from another server that it was accessing while attempting to load the web page or fill another request by the browser.