Error 503

HTTP error 503 occurs when your origin web server is overloaded.

Common causes

There are different causes identifiable by the error message or the location of the error:

• Error does not contain cloudflare or cloudflare-nginx in the HTML response body. In this case, the issue is likely from your origin server.
• Error contains cloudflare or cloudflare-nginx in the HTML response body. In this case, the issue may stem from Cloudflare.
• Error is only visible in logs or analytics.

Resolution

To resolve a 503 error, first determine whether the issue originates from your origin web server or Cloudflare. The following sections provide guidance on troubleshooting both scenarios.

503 Error without cloudflare or cloudflare-nginx

If the error does not contain cloudflare or cloudflare-nginx in the HTML response body, contact your hosting provider to verify if they rate limit requests to your origin web server.

503 Error with cloudflare or cloudflare-nginx

If the error contains cloudflare or cloudflare-nginx in the HTML response body, a connectivity issue occurred in a Cloudflare data center. Provide Cloudflare support with the following information:

• Your domain name
• The time and timezone of the 503 error occurrence
• The output of www.example.com/cdn-cgi/trace from the browser where the 503 error was observed (replace www.example.com with your actual domain and hostname)

503 Error only visible in logs and analytics

These errors result from unsuccessful prefetches from Speed Brain and can be discarded. These errors are not visible to visitors of your website. Speed Brain can be disabled for the zone if needed (this feature cannot be disabled for a specific path).

Workers-specific causes

Error 503 can also occur when using Cloudflare Workers:

• A Worker exceeds CPU time limits (see Error 1102)
• Worker code encounters memory limit issues (see Error 1102)

If you are using Workers, check the Workers dashboard for error logs and resource limit issues.

Identifying the source of a 503 error

Use the error page content to determine whether a 503 was generated by Cloudflare or your origin server:

Cloudflare-generated 503

A Cloudflare-generated 503 indicates a connectivity issue in a Cloudflare data center. Refer to 503 Error with cloudflare or cloudflare-nginx for next steps, and check Security > Events for active mitigation events.

Origin-generated 503

If your origin generated a 503, check origin server logs for signs of overload: CPU/memory saturation, exhausted connection pool, or application-level maintenance mode.