The Error Budget is perhaps the most powerful concept in Site Reliability Engineering. It provides a data-driven way to manage the inherent tension between making changes and maintaining stability.
What is an Error Budget?
An Error Budget is the allowed amount of unreliability for a service. It is calculated as 100% minus your SLO. For example, if your availability SLO is 99.9%, your error budget is 0.1%. This budget represents the amount of time or number of requests that can fail before you violate your reliability target.
How Error Budgets are Used
Error budgets are used to make informed decisions about product development. If a service has a healthy error budget, the team can continue to deploy new features and take risks. However, if the error budget is exhausted, the team must prioritize reliability work, such as fixing bugs, improving automation, or addressing technical debt, until the budget is replenished.
The Benefits of Error Budgets
- Objective Decision Making: Moves away from subjective arguments about when to stop shipping features.
- Aligned Incentives: Both developers and SREs share the responsibility for the error budget.
- Controlled Risk: Allows teams to take calculated risks without compromising the user experience beyond agreed-upon limits.
Internal Links
Effective error budget management is a core part of our SRE Consulting. To understand the foundation of these budgets, read about What is an SLO?.
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