Description

This curriculum spans the technical and operational complexity of cache eviction in large-scale CDNs, comparable to the multi-phase rollout of a global caching strategy involving distributed systems engineering, security policy integration, and continuous performance optimisation across edge networks.

Module 1: Fundamentals of Caching and Eviction in CDNs

Select between time-based (TTL) and event-driven cache invalidation based on content update frequency and origin server load tolerance.
Configure TTL values per content type (e.g., HTML vs. images) considering consistency requirements and origin offload goals.
Implement stale-while-revalidate policies to serve expired content during origin fetch, balancing availability and freshness.
Evaluate the impact of cache hit ratio versus data staleness in high-traffic scenarios with frequently changing content.
Design cache key structures to include URL, query parameters, and headers such as Accept-Encoding to prevent incorrect content delivery.
Integrate health checks into caching logic to avoid serving stale content when origin servers are unreachable.

Module 2: Cache Eviction Algorithms and Selection Criteria

Compare LRU, LFU, and FIFO eviction behaviors under traffic patterns with skewed popularity distributions.
Implement adaptive eviction using ARC or LIRS when access patterns shift rapidly due to flash crowds or seasonal trends.
Adjust eviction thresholds based on object size to prevent large assets from disproportionately consuming cache space.
Monitor eviction rate per shard to detect anomalies indicating algorithm misconfiguration or unexpected traffic surges.
Introduce weighted eviction models that factor in object retrieval cost, popularity, and size for heterogeneous content.
Disable or modify eviction temporarily during origin server maintenance to prevent cascading failures upon restart.

Module 3: Distributed Caching and Cache Coherency

Deploy cache warming strategies across geographically distributed edge nodes after a global invalidation event.
Implement hierarchical cache invalidation using a pub/sub system to propagate purge commands from regional hubs to edge POPs.
Use versioned URLs or cache tags to enable bulk invalidation of related content without purging entire directories.
Design conflict resolution policies for edge caches when inconsistent states arise due to delayed invalidation messages.
Configure time-to-live synchronization between edge and origin to prevent premature evictions during network latency spikes.
Enforce idempotency in purge requests to avoid duplicate processing and message queue overloads in distributed brokers.

Module 4: Cache Invalidation Mechanisms and Operational Workflows

Choose between soft purge (mark as stale) and hard purge (remove immediately) based on origin resilience and user experience requirements.
Integrate CDN purge APIs into CI/CD pipelines to automate cache invalidation after content deployment.
Limit purge request rate per customer to prevent accidental or malicious cache flooding that degrades performance.
Log all purge operations with metadata (initiator, target, timestamp) for audit and forensic analysis during outages.
Validate purge success across all edge locations using synthetic monitoring probes post-invalidation.
Implement purge request batching to reduce control plane overhead during large-scale content updates.

Module 5: Capacity Planning and Memory Management

Allocate cache memory per POP based on historical traffic volume, peak concurrency, and content size distribution.
Set memory watermark levels to trigger proactive eviction before reaching capacity, avoiding sudden performance drops.
Segment cache storage by content class (static, dynamic, user-specific) to isolate performance impact during eviction.
Monitor memory fragmentation in object caches and schedule compaction during low-traffic periods if needed.
Use object pinning selectively for critical assets (e.g., login pages) to prevent eviction during high churn.
Balance SSD and RAM caching layers by routing frequently accessed small objects to in-memory stores and larger ones to disk.

Module 6: Monitoring, Logging, and Performance Tuning

Instrument cache hit ratio, byte hit ratio, and eviction rate per POP and content category for performance baselining.

Correlate spikes in origin fetches with recent configuration changes or purge events to identify misbehaving rules.

Configure real-time alerts for abnormal eviction patterns, such as sudden drops in hit ratio or high stale-serving rates.

Use trace logging to reconstruct cache state during incident postmortems involving stale or missing content.

Conduct A/B tests on eviction algorithms using shadow traffic to measure impact before full rollout.

Aggregate and analyze cache logs to detect long-tail content that consumes space without sufficient reuse.

Module 7: Security, Compliance, and Policy Enforcement

Restrict purge API access using role-based authentication and IP allowlists to prevent unauthorized cache manipulation.
Ensure GDPR-compliant cache handling by excluding PII from caching or enabling rapid purging upon data subject requests.
Enforce cache exclusion policies for sensitive endpoints (e.g., /account, /checkout) via automated configuration checks.
Encrypt cached content at rest on disk when regulatory requirements mandate data protection in edge storage.
Validate that cache headers from origin servers are sanitized to prevent unintended caching of private or session-specific data.
Implement audit trails for all cache policy changes, including TTL modifications and eviction rule updates.

Module 8: Advanced Eviction Strategies and Edge Cases

Handle conditional requests (If-None-Match, If-Modified-Since) correctly after eviction to avoid unnecessary origin fetches.
Manage cache behavior for A/B testing variants by including experiment identifiers in cache keys and purge scopes.
Prevent cache stampedes by introducing randomization in revalidation retries after mass eviction events.
Design fallback mechanisms for when eviction logic fails, such as periodic cache sweeps based on last-access time.
Optimize cache eviction in multi-tenant CDNs by isolating tenant workloads and applying per-tenant eviction quotas.
Simulate edge cache failures in staging environments to test eviction resilience under partial network partition.