Error budget = 100% − SLO — the allowed unreliability. A 99.9% SLO allows ~0.1% (~43 min/month) of failure. If the budget is healthy, ship features faster; if it is exhausted, freeze risky changes and focus on stability.

Detailed Answer

The error budget turns reliability into a shared, objective decision tool that balances feature velocity against stability. Teams spend the budget on releases and risk; when it runs out, a change freeze (feature deployments stop, only stability work) protects the SLO. This aligns dev and ops around one number instead of arguing about "how much testing is enough".

Code Example

# Error Budget = 100% - SLO
# SLO 99.9%  ->  budget 0.1%  ~  43.2 min / month

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Interview Tip

Give the formula and the 43 min/month figure, and explain the freeze-when-exhausted policy — that operational use is the point.

sreerror-budgetslo

What is an error budget and how does it drive decisions?

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