Escaping Cache Fragmentation: How Misconfigured PHP Workers Flooded My Token System

🚨 The Symptom I started noticing something strange in my observability stack: Integration tokens were being minted repeatedly My token endpoint showed activity even when no user interaction was happening Metrics suggested constant “traffic” to an otherwise idle system At first glance, it looked like: A security issue A rogue client Or a broken API consumer It was none of those. 🔍 The Root Cause The issue came down to a subtle but critical architectural mistake: I was using a non-shared cache in a multi-worker environment. Stack involved: PHP-FPM (2 workers) APCu (in-memory cache) Token-based integration between services ⚙️ What Went Wrong APCu is process-local , not shared. That means: Worker A cache ≠ Worker B cache Each PHP-FPM worker had its own isolated memory. 💥 The Cascade Effect My token logic was straightforward: if token not in cache : mint_new_token () But in reality, the system behaved like this: Request hits Worker A → token exists → OK Next request hits Worker B → cache mi