Troubleshooting Cloudflare 5XX errors – Cloudflare Help Center
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.
Required error details for hosting provider
When contacting your hosting provider, give them the following information:
- Specific 5XX error code and message.
- Time and timezone the 5XX error occurred.
- URL that resulted in the HTTP 5XX error (for example:
The error cause is not always found in the origin server error logs. Check logs of all load balancers, caches, proxies, or firewalls between Cloudflare and the origin web server.
Additional details to provide to your hosting provider or site administrator are listed within each error description below. Cloudflare change the appearance of default error pages discussed in this article.
Error Analytics per domain are available within . Error Analytics allows insight into overall errors by HTTP error code and provides the URLs, source IP addresses, and Cloudflare data centers needed to diagnose and resolve the issue. Error Analytics are based on a 1% traffic sample.
To view Error Analytics:
- Log in to the Cloudflare dashboard.
- Click the appropriate Cloudflare account for your site, then pick the domain.
- Next, click the Analytics & Logs app icon.
- Click Add filter, select Edge status code or Origin status code and choose any 5xx error code that you want to diagnose.
Error 500: internal server error
- Your domain name
- The time and timezone of the 500 error occurrence
- The output of from the browser where the 500 error was observed (replace with your actual domain and hostname)
Error 502 bad gateway or error 504 gateway timeout
An HTTP 502 or 504 error occurs when Cloudflare is unable to establish contact with your origin web server.
There are two possible causes:
502/504 from your origin web server
Cloudflare returns an 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 504 error originating from Cloudflare appears as follows:
- Time and timezone the issue occurred.
- URL that resulted in the HTTP 502 or 504 response (for example:
- Output from browsing to
Error 503: service temporarily unavailable
HTTP error 503 occurs when your origin web server is overloaded. There are two possible causes discernible by error message:
- Error doesn’t contain “cloudflare” or “cloudflare-nginx” in the HTML response body.
Resolution: Contact your hosting provider to verify if they rate limit requests to your origin web server.
- Error contains “cloudflare” or “cloudflare-nginx” in the HTML response body.
- Your domain name
- The time and timezone of the 503 error occurrence
- The output of from the browser where the 503 error was observed (replace with your actual domain and hostname)
Error 520: web server returns an unknown error
Error 520 occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.
- Origin web server application crashes
- not allowed at your origin
- Headers exceeding 16 KB (typically due to too many cookies)
- An empty response from the origin web server that lacks an HTTP status code or response body
- Missing response headers or origin web server not returning
upstream prematurely closed connection while reading response header from upstreamis a common error we may notice in our logs. This indicates the origin web server was having issues which caused Cloudflare to generate 520 errors.
- Full URL(s) of the resource requested when the error occurred
- Cloudflare cf-ray from the 520 error message
- Output from
- Two :
Error 521: web server is down
The two most common causes of 521 errors are:
- Offlined origin web server application
- Blocked Cloudflare requests
- Ensure your origin web server is responsive
- Review origin web server error logs to identify web server application crashes or outages.
- Confirm are not blocked or rate limited
- Allow all 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
- Find additional troubleshooting information on the .
Error 522: connection timed out
Error 522 occurs when Cloudflare times out contacting the origin web server. 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 15 seconds of Cloudflare sending a SYN.
- After a connection is established, the origin web server doesn’t acknowledge (ACK) Cloudflare’s resource request within 90 seconds.
- (Most common cause) are rate limited or blocked in .htaccess, iptables, or firewalls. Confirm your hosting provider allows Cloudflare IP addresses.
- An overloaded or offline origin web server drops incoming requests.
- 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.
- An from your origin web server to a 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
Error 523 occurs when Cloudflare cannot contact your origin web server. This typically occurs when a network device between Cloudflare and the origin web server doesn’t have a route to the origin’s IP address.
- 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 from your origin web server to a 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.
- If you use (deprecated) via a Cloudflare Hosting Partner, to troubleshoot the 523 errors.
- If you manage your (deprecated) installation, provide the following:
Error 524: a timeout occurred
Error 524 indicates that Cloudflare successfully connected to the origin web server, but the origin did not provide an HTTP response before the default 100 second connection timed out. This can happen if the origin server is taking too long because it has too much work to do - e.g. a large data query, or because the server is struggling for resources and cannot return any data in time.
Here are the options we’d suggest to work around this issue:
- Implement status polling of large HTTP processes to avoid hitting this error.
- 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.
- Enterprise customers can increase the 524 timeout up to 6000 seconds using the or using a with the
Proxy Read Timeoutsetting in the Cloudflare Dashboard.
- 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.
- If error 524 occurs for a domain using (deprecated), ensure the lan.timeout is set higher than the default of 30 seconds and restart the railgun service.
Error 525: SSL handshake failed
525 errors indicate that the SSL handshake between Cloudflare and the origin web server failed. Error 525 occurs when these two conditions are true:
- The fails between Cloudflare and the origin web server, and
- SSL is set in the Overview tab of your Cloudflare SSL/TLS app.
Contact your hosting provider to exclude the following common causes at your origin web server:
- No valid SSL certificate installed
- Port 443 (or other custom secure port) is not open
- No support
- The presented by Cloudflare to the origin do not match the cipher suites supported by the origin web server
- Check if you have a certificate installed on your origin server. You can check for more details on how to run some tests. In case you don’t have any certificate, you can create and install our free . Using Origin CA certificates allows you to encrypt traffic between Cloudflare and your origin web server.
- your server is using to ensure they match what is supported by Cloudflare.
- Check your server’s error logs from the timestamps you see 525s to ensure there are errors that could be causing the connection to be reset during the SSL handshake.
Error 526: invalid SSL certificate
Error 526 occurs when these two conditions are true:
- Cloudflare cannot validate the SSL certificate at your origin web server, and
- SSL is set in the Overview tab of your Cloudflare SSL/TLS app.
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 (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
- and visit
www.example.comwith your hostname and domain) to verify no issues exists with the origin SSL certificate:
Error 527: Railgun Listener to origin error
- Firewall interference
- Network incidents or packet loss between the Railgun server and Cloudflare
Common causes of 527 errors include:
If contacting Cloudflare support, provide the following information from the Railgun Listener:
- The full content of the railgun.conf file
- The full content of the railgun-nat.conf file
- Railgun log files that detail the observed errors
The following Railgun log errors indicate a connection failure between the Railgun Listener and your origin web server:
connection failed 0.0.0.0:443/example.com: dial tcp 0.0.0.0:443: i/o timeoutno response from origin (timeout) 0.0.0.0:80/example.com
Contact your hosting provider for assistance to test for connectivity issues between your origin web server and your Railgun Listener. For example, a netcat command tests connectivity when run from the Railgun Listener to the origin web server’s SERVERIP and PORT (80 for HTTP or 443 for HTTPS):
nc -vz SERVERIP PORT
LAN timeout exceeded
The following Railgun Listener log error is generated if the origin web server does not send an HTTP response to the Railgun Listener within the 30 second default timeout:
connection failed 0.0.0.0:443/example.com: dial tcp 0.0.0.0:443: i/o timeout
The time is adjusted by the lan.timeout parameter of the railgun.conf file.
Either increase the lan.timeout limit in railgun.conf, or review the web server configuration. Contact your hosting provider to confirm if the origin web server is overloaded.
The following errors appear in the Railgun logs when requests from the Railgun Listener are refused:
Error getting page: dial tcp 0.0.0.0:80:connection refused
Allow the IP of your Railgun Listener at your origin web server’s firewall.
TLS/SSL related errors
The following errors appear in the Railgun logs if TLS connections fail:
connection failed 0.0.0.0:443/example.com: remote error: handshake failureconnection failed 0.0.0.0:443/example.com: dial tcp 0.0.0.0:443:connection refusedconnection failed 127.0.0.1:443/www.example.com: x509: certificate is valid forexample.com, not www.example.com
If TLS/SSL errors occur, check the following on the origin web server and ensure that:
- Port 443 is open
- An SSL certificate is presented by the origin web server
- the SAN or Common Name of the origin web server’s SSL certificate contains the requested or target hostname
- SSL is set to in the Overview tab of the Cloudflare SSL/TLS app