> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gcore.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Common setup issues

> Fix common CDN setup issues like 503 errors, redirect loops, host header problems, file downloads, and SSL certificate errors.

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

## 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](/cdn/getting-started/configure-an-origin/add-cdn-servers-to-the-origin-acl-whitelist) 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](/cdn/troubleshooting/5xx-error-how-to-solve-server-issues) covers other origin and CDN server failures.

## 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:

**1. Open the CDN resource**

In the [Gcore Customer Portal](https://portal.gcore.com), navigate to **CDN** > **CDN resources** and open the resource.

**2. Open the access settings**

Navigate to **Access**.

**3. Disable the redirect**

Turn off **Enable redirect HTTP to HTTPS**.

**4. Apply the change**

Click **Save changes**.

The [HTTP to HTTPS](/cdn/cdn-resource-options/security/set-up-a-redirect-from-http-to-https) guide explains how to configure the CDN redirect when it is required.

## 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](/cdn/clear-cdn-resource-cache-by-url-pattern-or-all) and retest. See [Change Host header](/cdn/cdn-resource-options/http-headers/configure-and-check-the-host-header) for full configuration steps and how to verify the origin accepts the value.

## 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.

## 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](/cdn/troubleshooting/an-ssl-certificate-isn-t-working-how-to-solve-to-issue) covers other certificate validation and HTTPS delivery failures.