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Difficulty: MediumDefining and Managing SLOs, SLIs, and Error Budgets

A digital asset management platform operates a media processing API deployed on Google Cloud Run. The Site Reliability Engineering (SRE) team defines an availability Service Level Objective (SLO) of 99.95%99.95\% successful requests (HTTP non-5xx status codes) over a rolling 30-day measurement window. During a period where the service processed exactly 40,000,00040,000,000 total requests, an infrastructure outage caused 12,00012,000 request failures. How many additional failed requests can the API tolerate during this measurement window before completely exhausting its error budget?

Answer: 8000 failed requests

Answer

The service can tolerate an additional 8,000 failed requests before its error budget is completely exhausted.
For an availability SLO of 99.95%99.95\% on 40,000,00040,000,000 requests, the total error budget is 40,000,000×(1−0.9995)=20,00040,000,000 \times (1 - 0.9995) = 20,000 allowed error requests. Having already incurred 12,00012,000 errors, the remaining error budget is 20,000−12,000=8,00020,000 - 12,000 = 8,000 failed requests.

Step-by-Step Solution

1
Calculate the total allowable error budget in terms of request failures.
Total allowable error budget = 40,000,000×(1−0.9995)=20,00040,000,000 \times (1 - 0.9995) = 20,000 failed requests.
An availability SLO of 99.95%99.95\% allows an unreliability budget of 0.05%0.05\% (or 0.00050.0005) of total requests.
2
Calculate the remaining allowable error budget.
Remaining error budget = 20,000−12,000=8,00020,000 - 12,000 = 8,000 failed requests.
Subtracting the error budget already consumed by failures from the total budget yields the remaining capacity for bad requests.

Key Concept

Request-based Error Budget Calculation for Availability SLOs
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Topics

Defining and Managing SLOs, SLIs, and Error Budgets

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