Every few years, a team runs into the same wall. Their discount logic, eligibility checks, and fraud thresholds have become load-bearing code. They can't change a rule without touching a deployment. A sprint ticket. A code review. Someone's weekend.
So they go looking for a rules engine.
They implement Drools. Or they write their own YAML-driven decision tree. Or they drop Camunda into the stack. And two years later, the discount logic is still owned by engineering — it's just written in a different syntax now.
This is the part nobody warns you about. Open-source rules engines solve the technical problem of separating logic from application code. They don't solve the organizational problem of who still has to touch it.
What a Business Rules Engine Actually Is
