Database Connection Pool Blew Up Mid-Traffic-Shift: 6 Production-Grade Decisions for Blue-Green and Canary Deployment with Traffic Governance
Overview 2 AM. A ride-hailing platform’s payment service does a blue-green switch. The on-call engineer runs kubectl rollout to flip the Service selector, shifting traffic from blue to green. Everything looks fine — Pods are Ready, health checks pass, response latency looks normal. Three minutes later, the DBA chat explodes. Database connections spike from 200 to 1,200, the connection pool is maxed out, and five downstream services all time out. Root cause: the green environment’s app version updated the ORM framework, and the default pool size jumped from 20 to 100....