Effectively cache AEM Dispatcher

To optimize AEM Dispatcher caching effectively, there are several strategies to manage how content is cached and updated. The primary goals are to reduce load on the AEM Publisher instances and deliver faster response times to users by serving cached content whenever possible. Here’s an expanded view on how to configure AEM Dispatcher caching for optimal performance:

1. Caching Rules and Filters

  • Defining Caching Rules: Dispatcher allows you to define which resources should be cached and which should not. Typically, HTML pages, CSS, JavaScript, and images are cached, whereas dynamic assets like forms or data-driven pages are excluded.
  • Configuring Filters: Filters are essential in controlling access to the AEM Publisher. By defining filters, you can exclude requests that should not be cached, such as authentication pages, user-specific content, or data that changes frequently. In the dispatcher.any configuration file, you set up a series of allow/deny rules to define which URLs are cached.
  • Cache Time-to-Live (TTL) Settings: Configure TTL settings for various resources to control how long they remain in the cache. For example, static assets like images and CSS files may have a long TTL, while content pages may need shorter TTLs if they are updated more frequently. Setting the TTL too high on dynamic content can lead to serving outdated content, so it’s essential to align it with the content update frequency.

2. Dispatcher Flush for Dynamic Content

  • Dispatcher Flush Agent: Configure a Dispatcher Flush Agent on the AEM Publisher to handle cache invalidation efficiently. When content is activated or deactivated, the Dispatcher Flush Agent sends a request to Dispatcher, instructing it to remove specific pages or folders from the cache. This ensures only the necessary cached items are updated without clearing the entire cache.
  • Selective Cache Invalidation: Avoid full cache flushes for every content update. By invalidating only the pages that have changed, you can keep the cache hit ratio high and reduce load on the AEM Publisher. This requires setting up detailed cache invalidation rules, typically configured in the dispatcher.any file.
  • Flush on Demand: For pages that update dynamically based on user interactions or data sources, configure Dispatcher to flush these pages from the cache only when specific triggers occur. For instance, if a product catalog is updated nightly, you could set a flush rule to clear that specific content nightly.

3. Handling Dynamic Pages and Personalized Content

  • Using Headers for Dynamic Content: For pages that have both static and dynamic elements, you can leverage DispatcherPassThrough rules to allow certain requests (like AJAX calls) to bypass caching. This way, the core page remains cached, while dynamic elements are fetched directly from the AEM Publisher.
  • Tokenized and Personalized URLs: For pages personalized per user session or tokenized (e.g., URLs with query parameters), configure Dispatcher to differentiate these URLs in the cache or selectively bypass caching. Use path and query rules in Dispatcher to ensure dynamic content doesn’t get cached accidentally or served incorrectly to other users.

4. Improving Cache Performance

  • Enable Compression: Configure Dispatcher to cache compressed versions of resources, such as HTML, CSS, and JavaScript. This reduces bandwidth usage and delivers content faster to users.
  • Preloading Cache: Pre-cache high-traffic pages to reduce initial load times for end users. This can be automated through scripts that access frequently used pages, warming up the cache after deployments or maintenance.
  • Avoiding Over-Invalidation: Be cautious of invalidating entire cache directories when updating specific content. Configure rules to ensure only the necessary pages or sections are flushed to maintain a high cache hit rate.

5. Monitoring and Optimization

  • Logging and Metrics: Regularly monitor the Dispatcher cache logs to check cache hit and miss ratios, which will help identify areas that may need adjustment. For example, if you observe a high miss rate for certain resources, you might need to adjust cache rules for these assets.
  • Testing and Iteration: Continuously test cache rules, TTL settings, and flush strategies, adjusting them based on performance metrics and user behavior patterns.

By carefully tuning these Dispatcher caching settings, you can significantly reduce load on AEM Publisher instances and improve site performance, balancing cache longevity with the need for fresh content.

Back to blog