Q: Your team is adopting SRE practices. The VP asks you to define an "Error Budget" for a critical API. What is it, and how does it influence engineering decisions?

An Error Budget is the maximum amount of unreliability permitted over a time window, derived directly from the SLO (Service Level Objective).

• Error Budget = 100% – 99.9% = 0.1%
• In minutes: 30 × 24 × 60 × 0.001 = 43.2 minutes of allowed downtime per month
• Budget remaining (healthy): Engineering can deploy aggressively, run experiments, ship new features. The system can tolerate some failures.
• Budget exhausted (unhealthy): Feature releases are frozen. All engineering effort shifts to reliability improvements—fixing bugs, adding redundancy, improving monitoring.
• Shared accountability: Product teams and SRE teams share the same budget. Product managers understand that pushing risky features consumes reliability budget.

Calculation: If the SLO is 99.9% availability over 30 days: How it influences decisions: Practical implementation: The error budget transforms reliability from a vague goal into a measurable, actionable metric that balances innovation velocity with system stability.

• Track error budget burn rate on dashboards (Grafana/Datadog).
• Set alerts when 50%, 75%, and 90% of the budget is consumed.
• Automate deployment freezes when budget drops below a threshold.