The Closed-Loop Budget Brake: How a $5k Daily Cap Stopped 2 A.M. Compute Runaways

The 2 a.m. compute runaway is the canonical FinOps incident. A Spark job is misconfigured to provision new EMR nodes every minute it cannot find a leader. A test agent left running on a developer's laptop loops infinite Claude calls against the prod API key. An autoscaling group's max gets bumped from 20 to 2000 in a Terraform plan that nobody reviewed at the right line number. Everything is asleep. The hourly spend goes from $63 to $830 to $4,200. By 9 a.m. the team gets a Slack ping from finan...