When sticky sessions killed our payment platform performance

Ever wonder how a "performance optimization" can make your system 240% slower? Let me tell you about a European fintech platform that learned this lesson the hard way.

The problem: uneven load distribution

This payment processor handled 50,000+ daily transactions across 12 EU markets. Their setup looked reasonable: 6 application servers behind a load balancer with session affinity enabled. The theory was sound - keep users on the same server for better performance.

Reality hit during peak hours (8-10 AM). While some users breezed through transactions, others waited forever. The culprit?…