AEM Caching Strategy

Purpose

Design and implement multi-layer caching architectures spanning CDN, dispatcher, AEM in-memory caches, and application-level caches for optimal content delivery performance.

When to Use (Triggers)

• User mentions "caching," "cache invalidation," "cache strategy," or "TTL"
• References to dispatcher cache, CDN cache, Sling caching, or in-memory cache
• Questions about cache hit ratio, stale content, or cache warming
• Requests involving personalized content caching or edge-side includes
• Discussion of cache coherency, invalidation patterns, or cache hierarchy

Core Capabilities

• Design multi-tier caching architecture (CDN → Dispatcher → AEM → JCR)
• Configure TTL-based and event-based cache invalidation strategies
• Implement application-level caching for expensive computations
• Handle personalized content caching using Edge Side Includes (ESI) or client-side
• Optimize cache hit ratios across all caching layers

Domain Knowledge Required

Technical Foundation

• HTTP caching semantics (Cache-Control directives, Vary header, ETag, conditional requests)
• CDN architecture (edge caching, origin shield, cache keys, purge APIs)
• Cache invalidation patterns (TTL, event-based, tag-based, surrogate keys)
• Cache consistency models (eventual, strong, read-after-write)

AEM-Specific Context

• Dispatcher cache (file-based, stat file invalidation, auto-invalidation)
• AEM in-memory caches (Sling ResourceResolver cache, component output cache)
• Stat file level and its impact on invalidation scope
• Grace period configuration for serving stale content during refresh
• Client library fingerprinting for long-term asset caching

Implementation Approach

Step 1: Cache Architecture Design

Plan the caching layers and their responsibilities.

• Map content types to appropriate caching tiers
• Define TTL strategy per content type (static: days, pages: hours, API: minutes)
• Identify uncacheable content and alternatives (ESI, client-side, SDI)
• Plan cache key strategy (URL, headers, cookies that vary)

Step 2: CDN Configuration

Set up edge caching for global performance.

• Configure CDN caching rules per content type
• Set up surrogate keys or cache tags for targeted purge
• Implement origin shield to reduce load on dispatcher
• Configure WAF rules that don't break caching

Step 3: Dispatcher Cache Optimization

Maximize dispatcher cache effectiveness.

• Configure stat file level for granular invalidation
• Implement permission-sensitive caching where needed
• Set up cache warming after deployment or invalidation
• Configure grace period and serveStaleOnError

Step 4: Application-Level Caching

Implement in-AEM caching for expensive operations.

• Cache Sling Model computation results with TTL
• Implement query result caching for repeated queries
• Use Guava/Caffeine cache for service-level data caching
• Configure cache sizing based on available heap

Step 5: Invalidation Strategy

Implement coherent cache invalidation across all layers.

• Configure flush agents for dispatcher invalidation on publish
• Set up CDN purge triggers on content activation
• Implement tag-based invalidation for related content groups
• Design cache warming jobs post-invalidation

Quality Checklist

• [ ] CDN cache hit ratio > 95% for static assets
• [ ] Dispatcher cache hit ratio > 85% for page content
• [ ] No stale content visible beyond defined TTL
• [ ] Cache invalidation triggers within 30 seconds of publish
• [ ] Personalized content doesn't pollute shared cache
• [ ] Cache warming covers critical user paths after deploy
• [ ] Application-level caches bounded and don't cause OOM
• [ ] Monitoring in place for cache hit ratios across all layers

Related Skills

• aem-dispatcher-configuration (dispatcher cache details)
• aem-performance-tuning-profiling (performance measurement)
• aem-content-api-headless (API response caching)

Example Use Cases

1. E-commerce Product Pages: Implement multi-layer caching for 50,000 product pages with personalized pricing (client-side fetch), shared product details (dispatcher cache, 1h TTL), and static assets (CDN, 1y TTL with fingerprinting).
2. News Site with Breaking Content: Design caching strategy balancing freshness (5-minute TTL for homepage) with performance (long TTL for article pages), using Sling Dynamic Include for personalized sidebar content.
3. Global CDN with Regional Content: Configure CDN caching with Vary header on geo-location for region-specific content, surrogate key purging for content updates, and edge-side includes for user-specific navigation.

Notes

• Dispatcher cache is file-based — every cached response is a file on disk; monitor disk space
• Stat file invalidation invalidates entire subtrees — set stat file level carefully
• Never cache responses with Set-Cookie headers — this caches session identifiers
• AEM Cloud Service includes built-in CDN — configure via dispatcher rules, not separate CDN config