Troubleshooting 5xx Errors in Fasterize

Introduction

HTTP 5xx errors indicate a problem on the server side. They may be related to your origin server, the CDN, or the Fasterize platform itself. This guide helps you diagnose and resolve these errors based on the code you receive.

1. First and foremost: gather the right information

For any investigation, start by gathering the following information:

• The specific HTTP error code (e.g., 500, 504, 524)
• Therelevant URL
• Theexact time (including time zone)
• The browser'sIP address
• Useful HTTP headers (e.g., X-Fstrz, X-unique-id, Request ID)

💡 This information is essential for your hosting provider or Fasterize support. How do I retrieve the requestID?

2. Server-side errors

🔧 500: Internal Server Error

A 500 error indicates a problem with your origin web server. Error establishing a database connection is a common HTTP 500 error message generated by your origin web server.

In this case, Fasterize was able to connect to the origin server but received a 500 error in response. The HTTP response header X-Fstrz added by Fasterize then has the value stc, Z, p.

💡 Note: To simplify incident resolution, Fasterize does not use error code 500.

Resolution:

• Provide your hosting provider with detailed information so they can help you resolve the issue. This is usually an application error.

🔧 502 / 504: Bad Gateway / Gateway Timeout (from the origin)

An HTTP 502 or 504 error can occur in two ways:

• when the error is generated by your origin web server
• when our CDN is unable to establish a connection with the optimization engine

502/504 from your origin web server

In this case, Fasterize was able to establish a connection to the origin, but the origin returned a response with error code 502 or 504. The returned page does not mention Fasterize or any CDN (e.g., CloudFront). The header X-Fstrz is then equal to stc, Z, p.

Resolution:

• Contact your hosting provider to determine the cause:
  • Verify that the origin server responds to requests for the hostname and domain of the URL being visited.
  • Check for excessive server load, crashes, or network outages.
  • Identify any blocked or expired applications or services.

🔧 503: Service Unavailable

HTTP error 503 occurs when your origin web server is overloaded. This status code is never returned by Fasterize. As with 500 errors, the header X-Fstrz is equal to stc, Z, p or etc., Z, p.

Resolution:

• Contact your hosting provider to check whether they are throttling bandwidth or if your server is undergoing maintenance.

🔧 542: Unable to connect to the origin

Fasterize returns a 542 error when it is unable to access the origin web servers. There are several possible reasons for this:

• The origin server specified in the configuration is incorrect
• The server is down or unavailable
• It blocks connections from Fasterize
• The TLS certificate is invalid
• TLS negotiation failed (incompatible TLS ciphers)
• DNS resolution fails

Resolution:

• Contact the site administrator or the web host to:
  • Check the configuration
  • View the error logs
  • Make sure that Fasterize IP addresses are not blocked
  • Whitelist Fasterize IP ranges

🔧 544: Slow response from the origin

An error 544 is generated if Fasterize is unable to connect to the origin server within 20 seconds, or if no HTTP response is received within 175 seconds.

Resolution:

• Contact your hosting provider to rule out the following causes:
  • Long-running process on the server (e.g., catalog export)
  • Server overload
• Check the logs (Apache, Nginx) to identify the causes of slow performance
• If necessary, run these processes outside of Fasterize (on a non-proxied subdomain)

3. Errors on the CDN or Fasterize side

🌐 502 / 504: from the CDN (e.g., CloudFront)

Error 502/504 displayed by the CDN when it is unable to contact Fasterize.

Resolution:

• Visit https://status.fasterize.com to check the service status
• If there are no issues, contact support with:
  • Exact time
  • Relevant URL
  • Number of Request ID
  • Browser IP address

⚙️ 521: Configuration not found

Error 521 means that the Fasterize platform was unable to find a configuration matching the domain name.

Resolution:

• Contact Fasterize Support with:
  • Time
  • URL
  • X-unique-id
  • IP address

🔁 524: Redirect loop

The origin of the configuration points to Fasterize instead of the origin server, causing a loop.

Resolution:

• Contact Fasterize Support with:
  • Time
  • URL
  • X-unique-id
  • IP address

🛠️ 53x / 59x: Fasterize internal error

An internal error has occurred on the Fasterize platform.

Resolution:

• Check out https://status.fasterize.com
• If no incidents are listed, contact support with:
  • Time
  • URL
  • X-unique-id
  • IP address

🧪 543: Prerender not available

This error may occur when Chrome performs a prerender using Speculation Rules. If the page is not cached on Fasterize, a 543 error is returned to prevent an unnecessary request to the origin.

Resolution:

• No impact on users
• Clicking will trigger a normal load
• Optional: Adjust the speculation rules if necessary

Conclusion

5xx errors can have various causes. This guide helps you identify the source of the problem and take action quickly. Always remember to provide the necessary information to speed up the diagnosis, whether you’re working with your hosting provider or our support team.

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