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Troubleshoot Azure Front Door file compression

Applies to: ✔️ Front Door Standard ✔️ Front Door Premium

This article helps you troubleshoot file compression issues in Azure Front Door.

Symptom

Compression is enabled for your route, but files are being returned uncompressed.

Tip

To check if your files are compressed, use a tool like Fiddler or your browser's developer tools. Look for the Content-Encoding header in the HTTP response. If it has a value of gzip, bzip2, or deflate, your content is compressed.

Content-Encoding header

Cause

Possible causes include:

  • The content isn't eligible for compression.
  • Compression isn't enabled for the file type.
  • The HTTP request lacks a valid compression type header.
  • The origin is sending chunked content.

Troubleshooting steps

Tip

Azure Front Door configuration changes can take up to 10 minutes to propagate. If this is your first time setting up compression, wait 1-2 hours to ensure settings have propagated to the POPs.

Verify the request

Use your browser's developer tools to check the requests:

  • Ensure the request is sent to <endpointname>.z01.azurefd.net, not your origin.
  • Ensure the request includes an Accept-Encoding header with gzip, deflate, or bzip2.

CDN request headers

Verify compression settings

In the Azure portal, navigate to your endpoint and select Configure in the Routes panel. Ensure compression is enabled.

CDN compression settings

Check the request at the origin server for a Via header

The Via header indicates a proxy server. By default, Microsoft IIS servers don't compress responses with a Via header. To override this:

  • IIS 6: Set HcNoCompressionForProxies="FALSE" in the IIS Metabase properties. See IIS 6 Compression.
  • IIS 7 and up: Set noCompressionForHttp10 and noCompressionForProxies to False in the server configuration. See HTTP Compression.

Next steps

For more information, see Azure Front Door FAQ.