Troubleshooting Cloudflare 5XX errors

When troubleshooting most 5XX errors, the correct course of action is to first contact your hosting provider or site administrator to troubleshoot and gather data. The following sections outline:

• The information to provide your hosting provider to help resolve the errors
• The steps to access error analytics in the Cloudflare dashboard.

Note

Cloudflare Support only assists the domain owner to resolve issues. If you are a site visitor, report the problem to the site owner.

Required error details for hosting provider

When contacting your hosting provider, share the following information:

• The specific 5XX error code and message.
• The time and timezone when the 5XX error occurred.
• The URL that resulted in the HTTP 5XX error (for example, https://www.example.com/images/icons/image1.png).

The cause of the error is not always found in the origin server's error logs. Be sure to check the logs of any load balancers, caches, proxies, or firewalls between Cloudflare and the origin web server.

Additional details to provide to your hosting provider or site administrator can be found in the error descriptions below. Note that Cloudflare Custom Error Pages can alter the appearance of default error pages discussed in this page.

Error analytics

Error analytics per domain are available within Zone Analytics. Error analytics provides insights into overall errors by HTTP error code and offers details such as the URLs, source IP addresses, and Cloudflare data centers needed to diagnose and resolve issues. Error Analytics are based on a 1% traffic sample.

To view Error Analytics:

1. Log in to the Cloudflare dashboard ↗.
2. Select your account and domain.
3. Go to Analytics & Logs.
4. Select Add filter, select Edge status code or Origin status code and choose any 5xx error code that you want to diagnose.

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Error 500: internal server error

This error indicates a problem with your origin web server, preventing it from fulfilling the request.

Common causes

The Error establishing database connection message is a common HTTP 500 error, typically indicating an origin web server issue. If you encounter this error, contact your hosting provider for assistance.

Resolution

When dealing with most 5XX errors, the first step is to reach out to your hosting provider or site administrator to help troubleshoot the issue. Share the necessary error details to your hosting provider to assist troubleshooting the issue.

However, if the 500 error contains cloudflare or cloudflare-nginx in the HTML response body, contact Cloudflare support and provide the following details:

• Your domain name
• The time and timezone of the 500 error occurrence
• The output of www.example.com/cdn-cgi/trace from the browser where the 500 error was observed (replace www.example.com with your actual domain and hostname)

Note

If you observe blank or white pages when visiting your website, confirm whether the issue occurs when temporarily pausing Cloudflare and contact your hosting provider for assistance.

Error 502 bad gateway or error 504 gateway timeout

An HTTP 502 or 504 error indicates that Cloudflare is unable to establish contact with your origin web server.

Common causes

There are two possible causes:

• 502/504 errors from your origin web server (most common).
• 502/504 errors from Cloudflare.

You may also see 504 status codes in logs or analytics caused by cache MISS responses from Early Hints.

Resolution

To resolve 502/504 errors, it is essential to identify whether the issue originates from your origin web server or Cloudflare. In the following sections, you can find more details for troubleshooting and resolving errors from both sources.

502/504 from your origin web server

Cloudflare returns a Cloudflare-branded HTTP 502 or 504 error when your origin web server responds with a standard HTTP 502 bad gateway or 504 gateway timeout error:

Contact your hosting provider to troubleshoot these common causes at your origin web server:

• Ensure the origin server responds to requests for the hostname and domain within the visitor's URL that generated the 502 or 504 error.
• Investigate excessive server loads, crashes, or network failures.
• Identify applications or services that timed out or were blocked.

502/504 from Cloudflare

A 502 or a 504 error originating from Cloudflare appears as follows:

If the error does not mention cloudflare, contact your hosting provider for assistance. Refer to 502/504 errors from your origin for more information.

This error can occur due to a compression issue at the origin, such as when the origin server serves gzip-encoded compressed content but fails to update the content-length header, or if the origin is serving broken gzip compressed content. To diagnose this, you can try disabling compression at your origin to confirm if it resolves the error.

Additionally, in some cases, a particular data center may experience a sudden increase in traffic. To ensure minimal impact for customers, our automated processes will redirect traffic to another data center. These adjustments typically happen seamlessly and take just a few seconds. However, during this process, some clients may experience temporary latency or HTTP 502 errors. You can find more information about our automated traffic management tools in this blogpost ↗.

If you need further assistance from our Support team, provide the following details to Cloudflare Support to avoid delays in processing your inquiry:

• The time and timezone when the issue occurred.
• The URL that resulted in the HTTP 502 or 504 response (for example, https://www.example.com/images/icons/image1.png).
• The output from browsing to <YOUR_DOMAIN>/cdn-cgi/trace.

Error 503: service temporarily unavailable

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

Common causes

There are two possible causes identifiable by the error message:

• 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.

Additionally, 503 status codes in logs or analytics may result from unsuccessful prefetches from Speed Brain.

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)

Error 520: web server returns an unknown error

This error occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.

Common causes

This error is often triggered by:

• Origin server crashes or misconfigurations.
• Firewalls or security plugins blocking Cloudflare IPs ↗ at your origin.
• Headers exceeding 16 KB (often due to excessive cookies).
• Empty or malformed responses lacking an HTTP status code or response body.
• Missing response headers or origin web server not returning proper HTTP error responses ↗.
• Incorrect HTTP/2 configuration at the origin server.

Note

520 errors are prevalent with certain PHP applications that crash the origin web server.

Resolution

Note

As a temporary workaround, you can set the affected DNS record to DNS-only in the Cloudflare DNS app or temporarily pause Cloudflare.

• Contact your hosting provider or site administrator and share the necessary error details to assist with troubleshooting. Request a review of your origin web server error logs for crashes and check for common causes mentioned in the previous section.

• If HTTP/2 is enabled at your origin server, ensure it is correctly set up. Cloudflare connects to servers who announce support of HTTP/2 connections via ALPN ↗. If the origin web server accepts the HTTP/2 connection but then does not respect or support the protocol, an HTTP 520 error will be returned. You can disable the HTTP/2 to Origin in Speed > Optimization > Protocol Optimization on the Cloudflare dashboard.

• If 520 errors continue after contacting your hosting provider or site administrator, provide the following information to Cloudflare Support:

  • Full URL(s) of the resource requested when the error occurred.
  • Cloudflare cf-ray from the 520 error message.
  • Output from http://<YOUR_DOMAIN>/cdn-cgi/trace.
  • Two HAR files:
    • One with Cloudflare enabled on your website.
    • Another with Cloudflare temporarily disabled.

Error 521: web server is down

Error 521 occurs when the origin web server refuses connections from Cloudflare. Security solutions at your origin may block legitimate connections from certain Cloudflare IP addresses ↗.

Common causes

The two most common causes of 521 errors are:

• Offlined origin web server application.
• Blocked Cloudflare requests.

Resolution

Contact your hosting provider or site administrator and share the necessary error details to assist in troubleshooting these common causes:

• Ensure your origin web server is responsive.
• Review origin web server error logs to identify web server application crashes or outages.
• Confirm Cloudflare IP addresses ↗ are not blocked or rate limited.
• Allow all Cloudflare IP ranges ↗ in your origin web server's firewall or other security software.
• Confirm that — if you have your SSL/TLS mode set to Full or Full (Strict) — you have installed a Cloudflare Origin Certificate or a certificate matching the requirements for these modes.
• Find additional troubleshooting information on the Cloudflare Community ↗.

Error 522: connection timed out

Error 522 occurs when Cloudflare times out contacting the origin web server.

Common causes

Two different timeouts cause HTTP error 522 depending on when they occur between Cloudflare and the origin web server:

• Before a connection is established, the origin web server does not return a SYN+ACK to Cloudflare within 19 seconds of Cloudflare sending a SYN.
• After a connection is established, the origin web server does not acknowledge (ACK) Cloudflare's resource request within 90 seconds.

Resolution

• Contact your hosting provider and share the necessary error details to assist in troubleshooting these common causes:

  • Cloudflare IP addresses ↗ are rate limited or blocked in .htaccess, iptables, or firewalls. Confirm your hosting provider allows Cloudflare IP addresses (most common cause).
  • An overloaded or offline origin web server drops incoming requests.
  • Keepalives ↗ are disabled at the origin web server.
  • The origin IP address in your Cloudflare DNS app does not match the IP address currently provisioned to your origin web server by your hosting provider.
  • Packets were dropped at your origin web server.

• If you are using Cloudflare Pages, verify that you have a custom domain set up and that your CNAME record is pointed to your custom Pages domain.

• If you are using Workers with a Custom Domain, performing a fetch to its own hostname will cause a 522 error. Consider using a Route or target another hostname instead.

• If none of the above leads to a resolution, request the following information from your hosting provider or site administrator before contacting Cloudflare support:

  • An MTR or traceroute from your origin web server to a Cloudflare IP address ↗ that most commonly connected to your origin web server before the issue occurred. Identify a connecting Cloudflare IP recorded in the origin web server logs.
  • Details from the hosting provider's investigation, such as pertinent logs or conversations with the hosting provider.

Error 523: origin is unreachable

This error occurs when Cloudflare cannot contact your origin web server.

Common causes

This typically occurs when a network device between Cloudflare and the origin web server does not have a route to the origin's IP address.

Resolution

Contact your hosting provider and share the necessary error details to exclude the following common causes at your origin web server:

• Confirm the correct origin IP address is listed for A or AAAA records within your Cloudflare DNS app.
• Troubleshoot Internet routing issues between your origin and Cloudflare, or with the origin itself.

If none of the above leads to a resolution, request the following information from your hosting provider or site administrator:

• An MTR or traceroute from your origin web server to a Cloudflare IP address ↗ that most commonly connected to your origin web server before the issue occurred. Identify a connecting Cloudflare IP from the logs of the origin web server.

Error 524: a timeout occurred

Error 524 usually indicates that Cloudflare successfully connected to the origin web server, but the origin did not provide an HTTP response before the default 100 seconds Proxy Read Timeout.

Common causes

This can happen if the origin server is taking too long because it has too much work to do, for example, a large data query, or because the server is struggling for resources and cannot return any data in time.

Error 524 can also indicate that Cloudflare successfully connected to the origin web server to write data, but the write did not complete before the 30 seconds Proxy Write Timeout (or 6.5 seconds in the case of Cloudflare Images).

Note

A 524 occurs if the origin web server acknowledges (ACK) the resource request after the connection has been established, but does not send a timely response.

Resolution

Here are the options we suggest to work around this issue:

• Implement status polling of large HTTP processes to avoid hitting this error.
• Contact your hosting provider to exclude the following common causes at your origin web server:
  • A long-running process on the origin web server.
  • An overloaded origin web server.

Note

Logging request response time at your origin web server helps identify the cause of resource slowness. Contact your hosting provider or site administrator for assistance in adjusting log formats or search for related logging documentation for your brand of web server such as Apache ↗ or Nginx ↗.

• Enterprise customers can increase the 524 timeout up to 6,000 seconds using the Edit zone setting endpoint (proxy_read_timeout setting). If your content can be cached, you may also choose to use a Cache Rule with the Proxy Read Timeout setting selected instead in the Cloudflare Dashboard.

Note

If the timeouts are on write requests, the Proxy Write Timeout of 30 seconds cannot be adjusted.

• If you regularly run HTTP requests that take over 100 seconds to complete (for example, large data exports), move those processes behind a subdomain not proxied (grey clouded) in the Cloudflare DNS app.

Note

Note that you may observe a 1 second difference between the timeout you have set and the actual time at which the Error 524 is returned. This is expected, it is due to the current work on implementing our proxy - Pingora ↗. As a workaround, you can simply set the timeout to one second more (121 seconds instead of 120 seconds, for example).

Error 525: SSL handshake failed

This error indicates that the SSL handshake between Cloudflare and the origin web server failed.

Common causes

Error 525 occurs when these two conditions are true:

• The SSL handshake ↗ fails between Cloudflare and the origin web server.
• Full or Full (Strict) SSL is set in the Overview tab of your Cloudflare SSL/TLS app.

Note

If your hosting provider frequently changes your origin web server's IP address, refer to Cloudflare's documentation on dynamic DNS updates.

Resolution

Contact your hosting provider to exclude the following common causes at your origin web server:

• No valid SSL certificate is installed.
• Port 443 (or another custom secure port) is not open.
• No SNI support.
• The cipher suites used by Cloudflare do not match the cipher suites supported by the origin web server.

Note

If 525 errors occur intermittently, review the origin web server error logs to determine the cause. Configure Apache to log mod_ssl errors ↗. Also, nginx includes SSL errors in its standard error log, but may possibly require an increased log level ↗.

• Verify that a certificate is installed on your origin server. For details on running tests, refer to Troubleshoot requests with curl. If no certificate is installed, you can generate and install a free Cloudflare origin CA certificate to encrypt traffic between Cloudflare and your origin web server.

• Review the cipher suites used by your server to ensure they are compatible with Cloudflare.

• Check your server's error logs from the timestamps when 525 errors occur to identify any issues causing the connection to be reset during the SSL handshake.

Error 526: invalid SSL certificate

This error indicates that Cloudflare is unable to verify the SSL certificate on your origin server, preventing a secure connection from being established.

Common causes

This error occurs when these two conditions are true:

• Cloudflare cannot validate the SSL certificate at your origin web server.
• Full SSL (Strict) SSL is set in the Overview tab of your Cloudflare SSL/TLS app.

Error 526 in the Zero Trust context

When using Cloudflare Gateway, an HTTP Error 526 might be returned in the following cases:

• An untrusted certificate is presented from the origin to Gateway. Gateway will consider a certificate is untrusted if any of these conditions are true:

  • The server certificate issuer is unknown or is not trusted by the service.
  • The server certificate is revoked and fails a CRL check.
  • There is at least one expired certificate in the certificate chain for the server certificate.
  • The common name on the certificate does not match the URL you are trying to reach.
  • The common name on the certificate contains invalid characters (such as underscores). Gateway uses BoringSSL ↗ to validate certificates. Chrome's validation logic ↗ allows non-RFC 1305 compliant certificates, which is why the website may load when you turn off WARP.

• The connection from Gateway to the origin is insecure. Gateway does not trust origins which:

  • Only offer insecure cipher suites (such as RC4, RC4-MD5, or 3DES). You can use the SSL Server Test tool ↗ to check which ciphers are supported by the origin.
  • Do not support FIPS-compliant ciphers (if you have enabled FIPS compliance mode). In order to load the page, you can either disable FIPS mode or create a Do Not Inspect policy for this host (which has the effect of disabling FIPS compliance for this origin).
  • Redirect all HTTPS requests to HTTP.

Error 526 in the Workers context

Workers subrequests to any hostname outside your Cloudflare zone that is not proxied by Cloudflare are always made using the Full (strict) SSL mode, regardless of the Workers zone configuration.

As a result, a valid SSL certificate is required at the origin server.

Resolution

Note

For a potential quick fix, set SSL to Full instead of Full (strict) in the Overview tab of your Cloudflare SSL/TLS app for the domain.

Request your server administrator or hosting provider to review the origin web server's SSL certificates and verify that:

• Certificate is not expired.
• Certificate is not revoked.
• Certificate is signed by a Certificate Authority ↗ (not self-signed).
• The requested or target domain name and hostname are in the certificate's Common Name or Subject Alternative Name.
• Your origin web server accepts connections over port SSL port 443.
• Temporarily pause Cloudflare and visit https://www.sslshopper.com/ssl-checker.html#hostname=www.example.com ↗ (replace www.example.com with your hostname and domain) to verify no issues exists with the origin SSL certificate:

If the origin server uses a self-signed certificate, configure the domain to use Full SSL instead of Full SSL (Strict). Refer to recommended SSL settings for your origin.

Error 530

This error indicates that Cloudflare is unable to resolve the origin hostname, preventing it from establishing a connection to the origin server.

Common causes

An HTTP error 530 is returned when Cloudflare is encountering an issue resolving the origin hostname. In this case the body of the response contains an 1XXX error code.

Resolution

Refer to the specific 1XXX error for troubleshooting information.