Preventing site downtime

Learn the features Cloudflare provides to keep your origin web server online, minimize downtime, and alert upon issues.


Cloudflare provides several features to help keep your site online and minimize downtime:

  • Zero-Downtime Failover
  • Standalone Health Checks
  • Passive Origin Monitoring

Zero-Downtime Failover

If your Cloudflare DNS provides another A or AAAA record or your Cloudflare Load Balancer lists another origin in the same pool, Zero-Downtime Failover automatically retries requests to your origin even before a Load Balancing decision is made.  Cloudflare currently retries only once for HTTP 521, 522, and 523 response codes. Zero-Downtime Failover is available on our Pro, Business, and Enterprise plans.

Standalone Health Checks

Health Checks monitor whether your website is reachable from Cloudflare’s edge network and  quickly notify of problems at your origin web server without requiring a Cloudflare Load Balancer.  Health Checks also provide analytics on the status changes for a specific health check and are available to domains on a Pro, Business, or Enterprise plan.

Cloudflare Load Balancing cannot leverage Health Checks as they are separate products. Similarly, Load Balancing Monitors cannot be converted to Health Checks.

Health Checks are a great alternative to Cloudflare Load Balancing if you only have one origin web server or don’t require balancing traffic across your infrastructure.

If an origin web server becomes unavailable, an email notification is sent to up to 20 emails you configure in the Health Check.  No alerts are sent if no email addresses are entered in the notification section for the Health Check.  

Configure Health Checks via the Cloudflare Traffic app under the Health Checks tab.

If a new Health Check is not working properly:
  • Consider checking the Follow Redirects option, or
  • if you are checking an HTTPS URL, consider checking the Allow Insecure option.


Health Checks have the following limitations per plan:

Check regions - The number of regions to check from:

  • Pro: 3
  • Business: 65535 
  • Enterprise: 65535

Health Checks - The number of allowed checks:

  • Pro: 10
  • Business: 50
  • Enterprise: 1000

Minimum Interval - The lowest allowed interval between checks

  • Pro: 60
  • Business: 15
  • Enterprise: 10

Passive Origin Monitoring

Cloudflare Passive Origin Monitoring notifies customers whenever their origin web servers are unreachable from Cloudflare’s edge network for 5 minutes and is available to all Cloudflare plans.  Passive Origin Monitoring 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.

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.

Configure email notifications

Alert emails are configured via the following procedure:

  1. Log into your Cloudflare account or click Account Home from your profile menu.
  2. Click Notifications.
  3. Click Create in the Notifications section.
  4. On the Create Notification page, enter a Name and Description and set Event to Passive Origin Monitoring.
  5. Add Notification emails.
  6. Click Save.

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. Alternatively, toggle Enabled to Off for the Passive Origin Monitoring Event listed under Manage Configured Notifications.

Disabling alerts affects every domain under your Cloudflare account regardless of the domain corresponding to the email alert you click to disable.


To resolve 521 errors, follow these recommendations:

Contact Cloudflare Support for assistance.

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