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How to Use HAProxy ACLs to Get URL Parameters

HAProxy is a reliable open-source software for high availability, load balancing, and proxying.

It offers different ways to manage and route traffic efficiently. One such method is `url_param(param_name)`, which lets us extract the value of a specific parameter from the URL query string.

Although this method doesn’t directly integrate with Access Control Lists (ACLs), we can use it in our configurations.

Additionally, HAProxy supports pattern matching within ACLs to manage URL parameters. Today we are going to take a look at both methods.

Using the url_param Fetch Method

The `url_param(param_name)` method in HAProxy is designed to fetch the value of a parameter named `param_name` from the URL query string. Also, this method is useful for routing decisions as per certain parameters in the URL.

Now, let’s look at an example where we check if a URL contains the `utm_source` parameter and route the request accordingly.

http-request
# Check if "utm_source" parameter exists
if url_param(utm_source) -m found
set-backend sales_server
# Otherwise, use default backend
else
use_backend default_backend


Here,

• The configuration checks if the `utm_source` parameter exists in the URL.
• If the parameter is found, the request goes to the `sales_server` backend.
• If the parameter is not found, the request goes to the `default_backend`.

This method helps direct traffic based on specific marketing campaign parameters embedded in URLs.

Matching URL Patterns with Parameters

Although `url_param` is useful, HAProxy also lets us define ACLs that match specific URL patterns containing desired parameters. This method leverages the path fetch method within ACLs for more granular control.

Now, let’s consider an example where we want to route traffic based on the presence of the `category=news` parameter in the URL.

# Allow access to URLs with "category=latest" parameter
acl latest_category path /latest?category= latest
use_backend latest_server if latest_category


Here,

• The latest_category ACL matches URLs with the path /latest and the query string containing category=latest.
• If a URL matches this pattern, the request goes to the `latest_server` backend.

This method is useful for directing traffic to different backends based on content categories or other URL parameters.

By combining these methods, we can boost the HAProxy configuration to manage traffic efficiently. This ensures that requests go to the backend servers as per URL parameters.

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Conclusion

In brief, our Support Experts demonstrated how to use HAProxy ACLs to get URL parameters.