Alibaba Cloud CDN returns standard HTTP status codes when errors occur. This reference describes every 4xx and 5xx code CDN may return, explains what each means in a CDN context, and lists concrete steps to resolve it.
4xx status codes
4xx codes indicate client-side errors. The request reached the CDN network but could not be fulfilled — either because of a problem in the request itself or because the client lacked the required permissions or credentials.
400 Bad Request
The origin server could not understand or process the request due to malformed syntax or invalid parameters.
Resolution: Check the request parameters for errors and resend.
401 Unauthorized
The request did not include valid authentication credentials. The origin server requires authentication before processing the request.
Resolution: Include valid authentication credentials and retry. If authentication is handled on the origin server, authorize the request there first.
403 Forbidden
The origin server understood the request but refused to fulfill it because the client does not have permission to access the resource.
Resolution: Grant the required permissions for the client, then retry.
404 Not Found
The origin server could not find the requested resource.
Resolution:
Verify the request path is correct.
Confirm the resource exists on the origin server.
Check whether the origin server's URL path is reachable from the internet.
405 Method Not Allowed
The origin server recognizes the resource but does not support the HTTP method used (for example, sending a POST to an endpoint that only accepts GET).
Resolution: Change the request to an HTTP method the origin server supports, then retry.
406 Not Acceptable
The origin server cannot return the resource in a format that satisfies the client's content negotiation headers (for example, Accept-Charset or Accept-Language).
Resolution: Update the request headers to specify content types and encodings the origin server supports, then retry.
407 Proxy Authentication Required
The client did not provide the authentication credentials required by the proxy server between the client and the origin.
Resolution:
Check whether the proxy origin server authentication has expired.
Include the correct credentials issued by the proxy origin server.
Retry the request.
408 Request Timeout
The origin server did not receive the complete request within its timeout window and closed the connection.
Resolution: Either extend the origin server's timeout period or reduce the request payload size, then retry.
409 Conflict
The request conflicts with the current state of the target resource. This often occurs with PUT requests when a client tries to update a resource that has changed since it was last retrieved.
Resolution: Refresh the resource, incorporate any changes, and resubmit. Alternatively, add conflict-handling logic on the origin server.
410 Gone
The resource has been intentionally and permanently removed from the origin server.
Resolution: Remove all references to the deleted resource in your client or application. Unlike 404, a 410 signals permanent removal — do not retry indefinitely.
411 Length Required
The request is missing the Content-Length header, which the origin server requires to process the request body.
Resolution:
If the content length is known, add
Content-Length: <size>to the request header.If the length cannot be determined in advance, use
Transfer-Encoding: chunkedinstead.
412 Precondition Failed
The origin server evaluated the conditional headers in the request (for example, If-Match or If-Unmodified-Since) and the precondition was not met.
Resolution: Update the request to include valid, current preconditions and retry.
413 Payload Too Large
The request payload exceeds the maximum size the origin server is configured to accept.
Resolution: Reduce the upload or submission size, then retry.
414 URI Too Long
The request URI is longer than the origin server is willing to process.
Resolution: Shorten the URI. If the request carries a large number of parameters, split them across multiple requests and aggregate the results on the client side.
415 Unsupported Media Type
The request payload is in a format the origin server does not support.
Resolution: Set Content-Type in the request header to a media type the origin server accepts, then retry.
416 Range Not Satisfiable
The Range header in the request specifies a byte range that falls outside the bounds of the resource.
Resolution: Verify the range in the Range header is valid for the resource size, correct it, and retry.
417 Expectation Failed
The origin server could not meet the expectation specified in the Expect request header.
Resolution: This code most commonly appears during testing. If it appears in production, disable the Expect field in the request header.
429 Too Many Requests
The client has exceeded the origin server's rate-limiting threshold within a given time window.
Resolution: Back off and retry after the interval indicated by the Retry-After response header (if present), or after the rate limit window set by the origin server resets.
499 Client Closed Request
The client closed the connection before the server finished processing the request and sending a response.
This typically happens when clients time out locally during slow operations — for example, large file uploads or long-running API calls. Because the client has already disconnected, it does not receive any error page.
5xx status codes
500 Internal Server Error
Your origin server encountered an internal error and could not process the request.
Resolution:
Check the origin server's error logs to identify the root cause.
If a recent deployment caused the error, roll back to the last working version to restore service.
Fix the underlying issue and confirm the origin is responding correctly before retrying.
502 Bad Gateway
A CDN POP could not connect to your origin server and received no valid response.
Resolution:
Confirm your origin server is running and reachable.
Check the origin server's firewall rules to make sure inbound traffic from CDN POPs is allowed.
Review the origin server logs for connection errors.
503 Service Unavailable
Your origin server is temporarily overloaded and unable to handle the request.
Resolution:
Check the load on your origin server to identify which application or process is consuming excessive resources.
504 Gateway Timeout
A CDN POP sent a request to your origin server but did not receive a response within the configured timeout period.
Resolution:
Confirm your origin server is available and reachable.
Check origin server performance — slow database queries or long-running processes can cause timeouts.
If the origin legitimately needs more time to respond, increase the timeout period as needed.
508 Loop Detected
A request forwarded by a CDN POP was redirected back into the CDN network, creating an infinite loop that exceeded the maximum redirect limit.
This typically happens when the origin server or a redirect rule sends traffic back to the CDN domain that initiated the request.
Resolution:
Check your origin server and any redirect rules for circular references.
Make sure every loop or redirect chain has a termination condition.
After fixing the loop, retry the request.