Error Budget
An error budget is the acceptable amount of failure for a service over a period, derived from its SLO, used to balance the pace of change against reliability.
An error budget is the amount of unreliability a service is permitted to incur over a given period before it breaches its service level objective. If an SLO targets 99.9 percent success, the error budget is the remaining 0.1 percent.
How It Works
The error budget is derived directly from the SLO: budget equals 100 percent minus the objective, applied over the SLO's time window. As real failures occur, measured by the service level indicator, they consume the budget. Teams track the remaining budget continuously. A common policy ties the budget to the pace of change: while budget remains, the team is free to ship new features and deploy frequently; once the budget is exhausted, change freezes or slows so that effort shifts to reliability work until the budget recovers.
Why It Matters
Error budgets resolve the natural tension between development, which wants to ship quickly, and operations, which wants stability. By quantifying acceptable risk, they replace arguments with a shared, data-driven rule. They also acknowledge that perfect reliability is wasteful: spending the budget on faster delivery is a legitimate choice. This framing is central to site reliability engineering and informs decisions about deployment frequency and incident response.
Related Terms
An error budget is computed from a service level objective and a service level indicator. It governs deployment frequency and triggers incident management when depleted.