How do I set cache expiration rules in a CDN?

Setting cache expiration rules in a CDN involves configuring Time To Live (TTL) values that determine how long content remains cached before refreshing. You access your CDN control panel, set appropriate expiration times for different content types, and use cache headers like Cache-Control and Expires to manage content freshness across your global network.

Understanding CDN cache expiration basics

Cache expiration rules control how long your content stays stored in CDN servers worldwide before being refreshed from your origin server. These rules form the foundation of effective content delivery by balancing performance optimization with content freshness.

When a user requests content, the CDN checks if a cached version exists and whether it has expired. If the cache is still valid, the CDN serves the stored version instantly. If expired, the CDN fetches fresh content from your origin server, caches it, and delivers it to the user.

Cache expiration directly impacts your website's loading speed, server bandwidth consumption, and user experience. Proper configuration reduces server load whilst ensuring users receive up-to-date content when necessary.

What are cache expiration rules and why do they matter?

Cache expiration rules are directives that specify how long different types of content should remain in CDN caches before being considered stale. These rules use TTL values measured in seconds, minutes, hours, or days to control content lifecycle.

These rules matter because they directly affect three critical aspects of web performance. Fast loading times occur when content serves from cache rather than origin servers. Reduced bandwidth costs result from fewer requests reaching your primary infrastructure. Improved user experience comes from consistent, speedy content delivery regardless of geographic location.

Without proper expiration rules, you risk serving outdated content or overwhelming your origin servers with unnecessary requests. Static assets like images can cache for months, whilst dynamic content might need hourly updates.

How do you configure cache TTL settings in your CDN?

Configure cache TTL settings by accessing your CDN provider's control panel and navigating to the cache configuration section. Most CDN platforms offer intuitive interfaces where you can set custom TTL values for different file types and URL patterns.

Start by identifying your content types and their update frequencies. Set longer TTL values for static assets like images, CSS files, and JavaScript libraries that rarely change. Configure shorter TTL values for dynamic content, API responses, and frequently updated pages.

Create rules based on file extensions or URL patterns. For example, set images (.jpg, .png, .gif) to cache for 30 days, stylesheets and scripts for 7 days, and HTML pages for 1 hour. Many CDN platforms allow you to create multiple rules with different priorities to handle complex caching scenarios.

What cache headers should you use for different content types?

Use Cache-Control headers as your primary method for managing cache behaviour across different content types. The Cache-Control directive offers precise control over how browsers and CDNs handle your content caching.

For static assets like images and fonts, use "Cache-Control: public, max-age=2592000" (30 days). The "public" directive allows caching by both browsers and CDNs, whilst "max-age" specifies the TTL in seconds.

For CSS and JavaScript files, implement "Cache-Control: public, max-age=604800" (7 days) combined with file versioning. This approach ensures users receive updates when you modify files whilst maintaining efficient caching for unchanged content.

Dynamic content requires more nuanced approaches. Use "Cache-Control: public, max-age=3600" (1 hour) for semi-static pages, or "Cache-Control: no-cache" for content requiring validation on each request. The Expires header provides fallback support for older systems but Cache-Control takes precedence when both exist.

How do you test if your cache expiration rules are working correctly?

Test your cache expiration rules using browser developer tools to examine response headers and verify cache status indicators. Open your browser's Network tab, load your website, and check the response headers for Cache-Control, Expires, and Age values.

Look for cache hit indicators in the response headers. Many CDN providers include custom headers like "X-Cache: HIT" or "CF-Cache-Status: HIT" that confirm content served from cache rather than origin servers.

Use online testing tools to verify cache behaviour from different geographic locations. These tools simulate requests from various CDN edge locations and display caching information, helping you identify configuration issues across your global network.

Monitor your CDN analytics dashboard for cache hit ratios. A healthy cache hit ratio typically ranges from 80-95%, depending on your content mix. Low hit ratios might indicate overly aggressive expiration rules or caching configuration problems.

Getting the most from your CDN cache configuration

Optimise your CDN cache configuration by implementing a layered caching strategy that balances content freshness with performance benefits. Start with conservative TTL values and gradually increase them based on your content update patterns and user behaviour analysis.

Avoid common mistakes like setting identical TTL values for all content types or using overly short expiration times that negate caching benefits. Don't cache user-specific content or frequently changing data for extended periods, as this can serve stale information to your users.

Implement cache purging strategies for urgent content updates. Most CDN platforms offer API-based purging that allows you to invalidate specific files or URL patterns when you publish critical updates outside normal TTL cycles.

Regular monitoring and adjustment improve your cache performance over time. Analyse your traffic patterns, content update frequencies, and user engagement metrics to refine your expiration rules and maximise the benefits of your CDN infrastructure.

At Falconcloud, we provide comprehensive CDN solutions with intuitive cache management tools that help you implement these best practices effectively across our global network of data centres.