Common setup issues

CDN setup issues commonly result from origin connectivity, redirect, response-header, or certificate-validation problems.

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503 service unavailable

During setup, a 503 response often indicates that the CDN cannot reach an available origin. Possible causes:

• The origin server is not accessible.
• The origin blocks CDN IP ranges.
• The origin port is incorrect.
• The resource has not fully propagated yet.

Solution:

• Verify that the origin server is reachable directly — with a browser or curl.
• Allowlist CDN servers in the origin firewall or ACL.
• Confirm that the configured origin port matches the port on which the origin listens. For ports other than 80 or 443, configure a custom origin port.
• During initial setup, CDN resource propagation can take up to about 20 minutes. Wait for propagation to finish, then retry the request.

The 5xx troubleshooting guide covers other origin and CDN server failures.

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ERR_TOO_MANY_REDIRECTS

This error can occur when both the CDN and the origin enforce redirects and create a loop. Possible cause:

• Both the CDN and the origin redirect HTTP to HTTPS.

Solution: Disable the redirect on either the CDN or the origin. To disable the CDN redirect: The HTTP to HTTPS guide explains how to configure the CDN redirect when it is required.

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Incorrect Host header

A misconfigured Change Host header option causes CDN nodes to forward requests to the origin with the wrong hostname, which the origin may handle incorrectly. Possible effects:

• Redirect loops or unexpected redirects — the origin redirects requests for an unrecognized hostname, which can interact with CDN redirects and produce a loop.
• 403 Forbidden responses — the origin rejects access for the hostname in the request.
• Dropped connections — the origin does not respond for the given hostname.

Solution: Open the CDN resource settings, go to HTTP headers > Host header, and enable Change Host header. Select the mode that matches how the origin identifies the incoming request:

• Custom Host header — enter the fixed hostname the origin virtual host expects. Use this when the origin serves a single site with a known host name.
• Forward Host header — CDN servers forward the Host header from the end-user request unchanged. Use this when the origin validates the incoming Host header against the request domain.

Click Save changes, then clear the cache and retest. See Change Host header for full configuration steps and how to verify the origin accepts the value.

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Website downloads as a file

This behavior usually means the origin returns incorrect response headers. Possible causes:

• The origin returns an incorrect Content-Type header.
• The origin returns a Content-Disposition: attachment header.

Solution:

• Check and correct the MIME type configuration on the origin server.
• Remove or correct the Content-Disposition header when content should display inline.

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SSL certificate errors (Let’s Encrypt)

SSL issues with Let’s Encrypt are often related to DNS configuration and domain validation. Possible causes:

• The custom domain CNAME does not point to the *.gcdn.co value shown in the CDN resource’s Setup guide.
• A CDN rule blocks, redirects, or otherwise interferes with validation requests to the /.well-known/acme-challenge/ path.
• DNS changes have not fully propagated.

Solution:

• Confirm that the custom domain CNAME matches the *.gcdn.co value shown in the CDN resource’s Setup guide.
• Keep /.well-known/acme-challenge/ accessible by narrowing interfering rules or adding an exception. If a rule was disabled for issuance, add the exception before re-enabling it so automatic renewal can complete.
• After DNS changes, wait for propagation to finish, then retry certificate issuance.

The SSL troubleshooting guide covers other certificate validation and HTTPS delivery failures.