HTTP 417 Expectation Failed vs 521 Web Server Is Down
HTTP 417 (Expectation Failed) is a 4xx Client Error response, while 521 (Web Server Is Down) is a 5xx Server Error response. 417 indicates that the server cannot meet the requirements of the Expect header. In contrast, 521 means that cloudflare-specific. The origin server refused the connection.
Description
The server cannot meet the requirements of the Expect header.
When You See It
When the server doesn't support Expect: 100-continue.
How to Fix
Remove the Expect header from your request.
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
417 is a 4xx Client Error response, while 521 is a 5xx Server Error response.
HTTP 417: The server cannot meet the requirements of the Expect header.
HTTP 521: Cloudflare-specific. The origin server refused the connection.
You encounter 417 when when the server doesn't support Expect: 100-continue.
You encounter 521 when when Cloudflare can't establish a TCP connection to the origin server.
When to Use Which
For 417 (Expectation Failed): Remove the Expect header from your request. For 521 (Web Server Is Down): Check that the origin server is running and the firewall allows Cloudflare IPs.