Azure Front Door URL Rewriting for Dynamic Paths

Arthur(Xueli) Wang 20

During the migration from Azure CDN to Azure Front Door, URL rewriting issues are being encountered. In Azure CDN, the pattern (.*) was used to replace matched content with a new address while preserving unmatched content and appending a SAS token. Now, with Azure Front Door, the requirement is to use {url_path:seg#} for matching.

The goal is to rewrite URLs, for example, changing /content/* to /media/pdf/*?<SAS token>. For fixed directories, a rule like /media/pdf/{url_path:seg1:2}?<sas token> works. However, for dynamic URL lengths, such as:

/content/1/2/3/4.pdf to /media/pdf/1/2/3/4.pdf?<sas token>
/content/1/2/3/4/5/6.pdf to /media/pdf/1/2/3/4/5/6.pdf?<sas token>

the current URL rewrite rules are not producing the desired results. What is the correct way to implement these rules in Azure Front Door?I have tried multiple URL rewrite rules, but they don't seem to work. Does anyone know how to write the rules?

Sai Prasanna Sinde 3,845 Reputation points Microsoft Vendor

2025-02-11T06:43:15.7933333+00:00
Hi @Arthur(Xueli) Wang

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

The below rule effectively rewrites the URL while preserving the dynamic path and appending the SAS token.

Source Pattern: /content/* (This matches any URL path starting with /content/)

Destination: /media/pdf/{url_path:seg1:99}?<SAS token>

/media/pdf/ : This is the fixed part of the new URL path.

{url_path:seg1:99} : This dynamically captures all segments of the URL path starting from the first segment (seg1) and continuing to the 99th segment. This effectively captures all remaining segments regardless of the URL length. By using seg1:99, you can capture all segments after /content/ regardless of their number, providing a solution for dynamic

URL lengths. ?<SAS token>: This appends the SAS token to the rewritten URL.

Make sure that the "Preserve unmatched path" option is set to "Yes" in your URL rewrite rule within the rule set. This ensures that any content after the matched pattern is retained in the rewritten URL.

Azure Front Door treats SAS tokens as query strings. Therefore, it is important to configure appropriate caching rules to prevent cached content from being accessible after the SAS token expires. You can achieve this by setting a cache duration that expires before the SAS token's expiration time.

While {url_path:seg#} is the primary method for URL path manipulation, Azure Front Door also supports other server variables and techniques for URL rewriting.

Kindly let us know if the above helps or you need further assistance on this issue.
Sai Prasanna Sinde 3,845 Reputation points Microsoft Vendor

2025-02-12T02:30:25.7933333+00:00

Hi @Arthur(Xueli) Wang,

Just checking in to see if you had a chance to see my response to your question.

Please tell us if it was helpful and let us know if you have any questions in the comments below so that we can address them.
Sai Prasanna Sinde 3,845 Reputation points Microsoft Vendor

2025-02-13T02:22:28.7566667+00:00

Hi @Arthur(Xueli) Wang,

Just checking in to see if you had a chance to see my response to your question.

Please tell us if it was helpful and let us know if you have any questions in the comments below so that we can address them.

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Azure Front Door URL Rewriting for Dynamic Paths

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