Apache HTTP Server
The world's most used web server software.
Apache HTTP Server powers a significant portion of the web ecosystem, but like any complex technology, it has its own unique set of challenges. When you encounter an error on this platform, it is rarely a random event. It is usually a specific response to a misconfiguration, a resource limit, or a compatibility issue. Our documentation for Apache HTTP Server is designed to cut through the noise. We don't just list the error codes; we explain the architecture behind them, helping you understand why the platform is rejecting your request or failing to load.
Common Errors
ERR_TOO_MANY_REDIRECTS
The ERR_TOO_MANY_REDIRECTS error, also known as a redirect loop, occurs when the website keeps redir...
Not Found
The 404 Not Found error is the most recognizable HTTP status code. It indicates that the server was ...
Internal Server Error
The 500 Internal Server Error is a generic catch-all response indicating that the server encountered...
403 Forbidden
The 403 Forbidden error indicates that the server understands the request but refuses to authorize i...
503 Service Unavailable
The 503 Service Unavailable error means the server is currently unable to handle the request due to ...
504 Gateway Timeout
The 504 Gateway Timeout error indicates that a server acting as a gateway or proxy did not receive a...
400 Bad Request
The 400 Bad Request error indicates that the server cannot or will not process the request due to so...
401 Unauthorized
The 401 Unauthorized error indicates that the request has not been applied because it lacks valid au...
405 Method Not Allowed
The 405 Method Not Allowed error indicates that the method received in the request-line is known by ...
429 Too Many Requests
The 429 Too Many Requests error indicates that the user has sent too many requests in a given amount...
ERR_SSL_PROTOCOL_ERROR
This error occurs when the browser cannot establish a secure connection to the server due to an issu...
Error 521 Web Server Is Down
This is a Cloudflare-specific error indicating that the origin web server refused the connection fro...
408 Request Timeout
The 408 Request Timeout error indicates that the server did not receive a complete request from the ...
505 HTTP Version Not Supported
The 505 HTTP Version Not Supported error indicates that the server does not support, or refuses to s...
Payload Too Large
The 413 Payload Too Large error indicates that the request entity is larger than limits defined by t...
Not Acceptable
The 406 Not Acceptable error occurs when a server is able to locate the requested resource but canno...
Unsupported Media Type
The 415 Unsupported Media Type error indicates that the server refuses to accept the request because...
Gone
The 410 Gone error is a permanent version of the 404 Not Found error. It indicates that the resource...
Web Server Returns an Unknown Error
Error 520 is a catch-all response from Cloudflare when the origin server returns something unexpecte...
URI Too Long
The 414 URI Too Long error indicates that the URL requested by the client is longer than the server ...
Length Required
The 411 Length Required error indicates that the server refuses to accept the request without a defi...
Precondition Failed
The 412 Precondition Failed error indicates that one or more conditions given in the request header ...
Range Not Satisfiable
The 416 Range Not Satisfiable error indicates that the server cannot serve the requested byte range ...
Expectation Failed
The 417 Expectation Failed error indicates that the server cannot meet the requirements of the Expec...
Not Implemented
The 501 Not Implemented error indicates that the server does not recognize the request method or lac...
SSL Handshake Failed
Error 525 indicates that the SSL handshake between Cloudflare and the origin web server failed. This...
Invalid SSL Certificate
Error 526 occurs when Cloudflare is set to 'Full (Strict)' SSL mode, but the origin server's SSL cer...
Unprocessable Entity
The 422 Unprocessable Entity error indicates that the server understands the content type of the req...
Conflict
The 409 Conflict error indicates that the request could not be completed due to a conflict with the ...
Insufficient Storage
The 507 Insufficient Storage error indicates that the server is unable to store the representation n...
Loop Detected
The 508 Loop Detected error indicates that the server terminated an operation because it encountered...
Proxy Authentication Required
The 407 Proxy Authentication Required error is similar to 401 Unauthorized, but it indicates that th...
Request Header Fields Too Large
The 431 Request Header Fields Too Large error indicates that the server is unwilling to process the ...
Bandwidth Limit Exceeded
The 509 Bandwidth Limit Exceeded error is a non-standard status code used by many shared hosting pro...
Network Authentication Required
The 511 Network Authentication Required error indicates that the client needs to authenticate to gai...
Locked
The 423 Locked error indicates that the resource that is being accessed is locked. This is a WebDAV-...
Failed Dependency
The 424 Failed Dependency error means that the request failed because it depended on another request...
Precondition Required
The 428 Precondition Required error indicates that the origin server requires the request to be cond...
Variant Also Negotiates
The 506 Variant Also Negotiates error indicates that the server has an internal configuration error:...
Not Extended
The 510 Not Extended error indicates that the policy for accessing the resource has not been met in ...
ERR_SSL_VERSION_OR_CIPHER_MISMATCH
This error happens when the browser and the server cannot agree on a common encryption protocol (SSL...
Unavailable For Legal Reasons
The 451 Unavailable For Legal Reasons error indicates that the server is denying access to the resou...
Misdirected Request
The 421 Misdirected Request error happens when a request is directed at a server that is not able to...
Upgrade Required
The 426 Upgrade Required error indicates that the server refuses to perform the request using the cu...
I'm a Teapot
The 418 I'm a Teapot error is an HTTP status code defined in RFC 2324 (Hyper Text Coffee Pot Control...
ERR_CONTENT_DECODING_FAILED
The ERR_CONTENT_DECODING_FAILED error occurs when the browser receives data from the server but cann...
ERR_SSL_OBSOLETE_VERSION
The ERR_SSL_OBSOLETE_VERSION error is a security warning in Chrome indicating that the website is us...
AH00558: Could not reliably determine the server's fully qualified domain name
This warning (not an error, but should be addressed) means Apache cannot definitively determine its ...
Client denied by access configuration
The AH01630 error indicates that Apache has been configured to deny access to a specific client (ide...
Request Entity Too Large
The AH00094 error indicates that the client attempted to send a request with a body (the data sent i...
Cannot allocate memory
The 'AH01071: Cannot allocate memory' error in Apache HTTP Server indicates that the system is unabl...
Syntax error on line X of Y: Z
This Apache error (AH00072) signifies a syntax error within one of the Apache configuration files. T...
Best Practices for Apache HTTP Server Stability
Maintaining a stable Apache HTTP Server environment requires proactive monitoring. Many of the errors listed above can be prevented by regular updates, proper caching configurations, and strict permission management. If you are a developer, ensure you are checking the platform's specific error logs, which often contain more detail than the public-facing error message.
Whether you are dealing with API rate limits, server timeouts, or authentication failures, the solutions provided here are tested and verified. Bookmark this page to have a quick reference guide whenever Apache HTTP Server throws an unexpected exception.