4xx errors could be caused by a malfunction on the Origin side or incorrect CDN-resource settings.

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Check the content availability on the origin source

Request the content from the origin source and ensure you get an HTTP 200 response code. If you use IP allowlist on the origin or a DDoS Protection service ensure that CDN-edges IPs are allowlisted. Use the API request above to get the list of Public IPs. 
curl -i -X GET https://api.gcore.com/cdn/public-ip-list
Since we constantly update the Public IP list, we recommend you run a script for the regular allowlist updating. You can also use HTTP Request Header for the authentication on your origin. You may find out more about the Origin ACL.

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Check your CDN resource’s settings

  • Ensure that the CDN resource is active. If you have created a new resource, wait until its configuration is applied on CDN-edges. Usually, it takes 15 minutes.
  • Ensure that Origin can respond to the requests from CDN edges by choosing Origin Pull Protocol. Learn more about this option from the article.
  • Check the Change Host Header option. Make sure that the option is active and the value is the same as the Origin Source or match with the host that you have set up on the Origin. You may find more information about Host Header. Go to the Reports tab to track the amount of 4xx errors.
To receive more details about users’ requests to resources, use the Raw logs option. It is a paid feature The Raw log receiving setup flow and the description of logs’ fields are located here. If you want to activate this feature, contact your account manager or send a request to technical support (support@gcore.com).