Optimizing CDN Caching with URL Normalization

In the world of content delivery networks (CDNs), efficient caching is crucial for performance and cost-effectiveness. However, many organizations face challenges with caching due to non-normalized URLs. This article explores a powerful solution using AWS CloudFront Functions to implement URL normalization, significantly improving caching efficiency.

The Problem: Caching Inefficiencies Due to Non-Normalized URLs

Many websites and applications suffer from caching inefficiencies caused by slight variations in URLs that point to the same content. These variations can lead to:

1. Duplicate content storage
2. Increased origin requests
3. Lower cache hit ratios

Common causes include:

• Inconsistent use of trailing slashes
• Variations in query parameter order
• Unnecessary or redundant query parameters
• Inconsistent encoding of URL components

The Solution: Comprehensive URL Normalization with CloudFront Functions

To address these issues, we've developed a robust URL normalization solution using CloudFront Functions. This approach standardizes both URL paths and query strings before they reach the cache, ensuring that slight variations are treated as the same URL.

Key Components of the Solution:

1. Path Normalization:

   • Convert backslashes to forward slashes
   • Merge multiple consecutive slashes
   • Apply RFC 3986 normalization for consistent percent-encoding

2. Query String Normalization:

   • Sort query parameters alphabetically
   • Remove empty parameters
   • Decode unnecessarily encoded characters
   • Standardize encoding (e.g., use '%20' for spaces instead of '+')

3. CloudFront Function Implementation:

   • Create a function that performs these normalizations
   • Apply the function to the Viewer Request event

Implementation Steps:

1. Log into the AWS Management Console
2. Navigate to the CloudFront console
3. Create a new CloudFront Function
4. Implement the normalization logic (code provided below)
5. Test the function with various URL scenarios
6. Deploy the function to your CloudFront distribution

The Code: URL Normalization CloudFront Function

function handler(event) {
    var request = event.request;
    var uri = request.uri;

    // Normalize backslashes to forward slashes
    uri = uri.replace(/\\/g, '/');

    // Merge successive forward slashes
    uri = uri.replace(/\/+/g, '/');

    // Remove trailing slash
    uri = uri.replace(/\/$/, '');

    // Normalize query string
    var querystring = request.querystring;
    if (typeof querystring === 'object' && querystring !== null) {
        var params = [];
        for (var key in querystring) {
            if (querystring.hasOwnProperty(key)) {
                var value = querystring[key].value;
                if (value !== undefined && value !== null && value.trim() !== '') {
                    key = normalizeQueryParam(key);
                    value = normalizeQueryParam(value);
                    params.push(key + '=' + value);
                }
            }
        }
        params.sort();
        querystring = params.join('&');
    }

    // Update the request object
    request.uri = uri;
    if (querystring) {
        request.querystring = querystring;
    }

    return request;
}

// Helper functions for URI and query parameter normalization
function normalizeUri(uri) {
    // Implementation details...
}

function normalizeQueryParam(param) {
    // Implementation details...
}
    

The Benefits:

By implementing this URL normalization solution, you can expect:

1. Increased cache hit ratio
2. Decreased origin requests
3. Improved overall performance and reduced latency
4. More predictable and manageable caching behavior
5. Potential cost savings from reduced data transfer and origin requests

Additional Optimization:

To further enhance caching efficiency, consider:

• Reviewing and adjusting your Cache Policy to include only relevant query parameters in the cache key
• Implementing an Origin Request Policy to control which parameters are forwarded to the origin

Conclusion:

URL normalization is a powerful technique for optimizing CDN caching efficiency. By leveraging CloudFront Functions to implement this solution, you can significantly improve your website's performance, reduce costs, and provide a better user experience. As web applications continue to grow in complexity, such optimizations become increasingly crucial for maintaining high-performance, scalable systems.

Remember to test thoroughly in a staging environment before deploying to production, and monitor your metrics to quantify the improvements in caching efficiency.