An error budget is the acceptable amount of unreliability. If your SLO is %, your error budget is %.
Monthly budget example:
- % availability = minutes of allowed downtime per month
- % = minutes
- % = minutes
How to use error budgets:
- Budget remaining: Ship features, take risks
- Budget exhausted: Freeze deploys, focus on reliability
Interview question: "How do you use error budgets to prioritize work?"
When budget is healthy, product velocity takes priority. When budget is low, reliability work takes priority. This removes the "reliability vs features" conflict.