Understand how Cloudflare alerts customers when their origin web servers are unreachable from Cloudflare for 5 minutes.
In July 2019, Cloudflare introduced a service to send email alerts to customers whenever their origin web servers become unreachable from Cloudflare’s edge network.
Cloudflare’s monitoring service reviews samples of origin web server HTTP responses for your visitor traffic. Alert emails are triggered when several circumstances are true:
- Your origin web server generated a non-5XX HTTP response within the past 24 hours,
- a recent 5 minute sample of traffic contains 100% HTTP 521 errors, and
- the errors account for >10% of traffic for the zone.
If your server periodically cycles (flaps) between returning 521 and non-521 HTTP responses, an alert is emailed only once per origin web server every 8 hours. Also, no more than 3 email alerts are sent for the same issue.
To disable origin monitoring alerts, click the link at the bottom of an alert email. A confirmation page appears if alerts are successfully disabled.
When using another proxy between Cloudflare and your origin web server (eg. Ezoic), the email alert from Cloudflare can show the IP address of the proxy service instead of your origin web server. This typically occurs if the proxy between Cloudflare and your origin web server returned the HTTP 521 errors.
To resolve 521 errors, follow these recommendations:
- Review the guide for troubleshooting 521 errors.
- Review Cloudflare’s Community Tips.
- Contact Cloudflare Support for assistance.