HTTP 520 Web Server Returned an Unknown Error vs 523 Origin Is Unreachable
Both HTTP 520 (Web Server Returned an Unknown Error) and 523 (Origin Is Unreachable) belong to the 5xx Server Error category. 520 indicates that cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process. Meanwhile, 523 means that cloudflare-specific. Cloudflare could not reach the origin server (DNS resolution failed or no route).
Description
Cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process.
When You See It
When Cloudflare receives an empty, unknown, or malformed response from the origin.
How to Fix
Check origin server logs. Ensure responses include proper headers. Verify SSL configuration.
Description
Cloudflare-specific. Cloudflare could not reach the origin server (DNS resolution failed or no route).
When You See It
When Cloudflare's DNS for the origin fails to resolve.
How to Fix
Verify DNS records in Cloudflare dashboard. Check origin server's IP address.
Key Differences
HTTP 520: Cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process.
HTTP 523: Cloudflare-specific. Cloudflare could not reach the origin server (DNS resolution failed or no route).
You encounter 520 when when Cloudflare receives an empty, unknown, or malformed response from the origin.
You encounter 523 when when Cloudflare's DNS for the origin fails to resolve.
When to Use Which
For 520 (Web Server Returned an Unknown Error): Check origin server logs. Ensure responses include proper headers. Verify SSL configuration. For 523 (Origin Is Unreachable): Verify DNS records in Cloudflare dashboard. Check origin server's IP address.