HTTP 204 No Content vs 521 Web Server Is Down
HTTP 204 (No Content) is a 2xx Success response, while 521 (Web Server Is Down) is a 5xx Server Error response. 204 indicates that the server successfully processed the request but is not returning any content. Common for DELETE operations and form submissions that don't need a response body. In contrast, 521 means that cloudflare-specific. The origin server refused the connection.
Description
The server successfully processed the request but is not returning any content. Common for DELETE operations and form submissions that don't need a response body.
When You See It
After DELETE requests, PUT updates where no body is needed, or CORS preflight responses.
How to Fix
No fix needed. The action was successful; there is simply no content to return.
Description
Cloudflare-specific. The origin server refused the connection.
When You See It
When Cloudflare can't establish a TCP connection to the origin server.
How to Fix
Check that the origin server is running and the firewall allows Cloudflare IPs.
Key Differences
204 is a 2xx Success response, while 521 is a 5xx Server Error response.
HTTP 204: The server successfully processed the request but is not returning any content. Common for DELETE operations and form submissions that don't need a response body.
HTTP 521: Cloudflare-specific. The origin server refused the connection.
You encounter 204 when after DELETE requests, PUT updates where no body is needed, or CORS preflight responses.
You encounter 521 when when Cloudflare can't establish a TCP connection to the origin server.
When to Use Which
For 204 (No Content): No fix needed. The action was successful; there is simply no content to return. For 521 (Web Server Is Down): Check that the origin server is running and the firewall allows Cloudflare IPs.