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HTTP 5xx codes can come from an error on an origin server or on CDN edge servers.

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Response-specific causes

The response code helps identify which origin behavior or CDN setting to investigate.
  • 500 Internal Server Error: Check the origin application and server logs for failures.
  • 502 Bad Gateway: Check for an invalid origin response, TLS or Server Name Indication (SNI) mismatch, or connection failure.
  • 503 Service Unavailable: Check whether the origin is unavailable or overloaded.
  • 504 Gateway Timeout: Check for an origin connection or read timeout.

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Gcore service status

If 5xx responses increase sharply or end users report widespread failures, the Status Page lists incidents or maintenance that affect:
  • CDN
  • Other Gcore services used as an origin (Object Storage, VPS, Dedicated Server, or Cloud)

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Origin server availability

Request content directly from the origin and inspect the response headers. For an HTTP origin that uses name-based virtual hosting, send the expected Host header:
For HTTPS, use --resolve to connect to the origin IP while preserving the hostname for the Host header and TLS SNI:
If the origin does not return the expected successful response, check its application and server logs or contact the hosting provider. An HTTP 504 response can occur when the origin exceeds the CDN timeout defaults — 5 seconds to establish a connection and 30 seconds between successive reads. On standard plans, custom timeouts can only reduce these limits, so they cannot resolve a slow origin; increasing the limits requires an Enterprise plan and assistance from Gcore Support. If access to the origin is restricted by IP or a DDoS Protection service, allowlist CDN edge IPs. Retrieve the current public IP list:
The public IP list changes over time, so keep the allowlist updated with a recurring script. The Origin ACL guide covers allowlisting CDN edges. Origin access control can also use request headers that the CDN adds when pulling content.

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CDN resource settings

Incorrect CDN resource settings can also cause HTTP 5xx errors. Review the common cases below.

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Incorrect Origin pull protocol

In the resource settings, select an Origin pull protocol that matches the protocol the origin uses. The Origin pull option controls which scheme the CDN uses when requesting content from the origin. For an HTTPS origin behind Cloudflare or CloudFront, keep Origin pull protocol set to HTTPS and configure Change SNI hostname with the hostname expected by that service. Select HTTP only when the origin is configured to accept unencrypted HTTP requests.

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Incorrect Host header

Enable Change Host header and set a value that matches the origin or the host configured on the origin. The Host header option controls which virtual host the origin uses. After changing Origin pull protocol, Change SNI hostname, or Change Host header, click Save changes before retesting the request.

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5xx response tracking and logs

The Response codes report tracks 5xx responses for CDN resources.
1

Open CDN

In the Gcore Customer Portal, select CDN.
2

Open CDN statistics

Navigate to Reports → Statistics.
3

View response codes

Select Response codes.
The Log viewer shows recent request details. For long-term log export, Logs uploader is a paid option that must be enabled by Gcore Support. To activate it, contact the account manager or Gcore Support. If you need to open a support ticket for a specific failed request, include the traceparent header from the CDN response if possible — it uniquely identifies the request and allows Gcore Support to locate it in Gcore systems. See Traceparent header for troubleshooting.