Apache Traffic Server 9.2.x cannot redirect `target` url to `replacement` url that contains a query-string

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04-10-2024

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Apache Traffic Server 9.2.x: The Challenge of Redirecting URLs with Query Strings

Apache Traffic Server is a powerful tool for optimizing web traffic, but it can sometimes be tricky to get everything working exactly as intended. One common challenge users face is redirecting a URL with a query string to another URL, also containing a query string. This article explores the issue and provides a clear solution for Apache Traffic Server 9.2.x.

The Problem:

Let's say you want to redirect the following URL:

http://www.example.com/old-page?id=123

To this URL:

http://www.example.com/new-page?id=123&param=value

You might try to achieve this by using the redirect command within your Traffic Server configuration. However, you'll quickly discover that simply using a command like this:

redirect /old-page http://www.example.com/new-page?id=123&param=value;

Won't quite work as intended. The redirection will happen, but the original query string (?id=123) will be lost.

Why is this happening?

Apache Traffic Server's redirect command essentially treats the entire target URL (including the query string) as a single unit. This means that the original query string is not preserved when redirecting to a URL with a different query string.

The Solution:

To solve this, you need to use Traffic Server's powerful url_remap functionality. The url_remap command allows you to manipulate the incoming URL, including its query string, in a much more granular way. Here's an example of how to achieve the desired redirection:

url_remap /old-page http://www.example.com/new-page?id=$1&param=value;

Explanation:

• /old-page: This is the URL pattern you want to match.
• http://www.example.com/new-page?id=$1&param=value;: This is the target URL.
  • The $1 is a placeholder for the first captured group from the original URL. In this case, it will capture the value of id from the original query string.
  • param=value is the new query string parameter you want to add.

This url_remap configuration will successfully redirect the original URL (http://www.example.com/old-page?id=123) to the target URL (http://www.example.com/new-page?id=123&param=value), preserving the original id value and adding the new param parameter.

Key Considerations:

• Regular Expressions: url_remap uses regular expressions, allowing you to define complex matching patterns.
• Capture Groups: Use $1, $2, etc. to capture and reuse values from the original URL.
• Multiple Parameters: You can add multiple query string parameters in the target URL using the & operator.

Conclusion:

Understanding how to use url_remap in Apache Traffic Server 9.2.x is crucial for effectively redirecting URLs, particularly when dealing with query strings. By leveraging the power of regular expressions and capture groups, you can easily control and manipulate the redirect behavior to suit your specific needs.

References:

• Apache Traffic Server Documentation
• Regular Expressions Tutorial