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

An enterprise IoT fleet management service runs its telemetry ingestion endpoint on Google Cloud Run. The Site Reliability Engineering (SRE) team has set a Service Level Objective (SLO) of 99.95%99.95\% availability over a rolling 30-day window (assuming 1 day = 24 hours). During the current 30-day period, an outage caused total service unavailability for 12 minutes, and a performance regression caused an error budget consumption equivalent to another 4 minutes of downtime. What is the remaining allowable downtime in minutes for this service within the 30-day window?

Answer: 5.6 minutes

Answer

The remaining allowable downtime is 5.6 minutes.
For a 30-day window, total minutes equal 30×24×60=43,20030 \times 24 \times 60 = 43,200 minutes. With an SLO of 99.95%99.95\%, the allowable downtime percentage is 0.05%0.05\%, giving a maximum allowable downtime of 43,200×0.0005=21.643,200 \times 0.0005 = 21.6 minutes. Since 1616 minutes (12+412 + 4) of error budget have already been consumed, the remaining allowable downtime is 21.6−16=5.621.6 - 16 = 5.6 minutes.

Step-by-Step Solution

1
Calculate the total duration of the rolling window in minutes.
30 days = 43,200 minutes.
The SLO is defined over a 30-day window, so error budget calculations must be based on the total minutes in that timeframe.
2
Calculate total allowable error budget in downtime minutes based on the 99.95% SLO.
Total allowable downtime = 21.6 minutes.
An SLO target of 99.95% permits an allowable unreliability percentage of 0.05%, which corresponds to 43,200 * 0.0005 = 21.6 minutes of downtime.
3
Subtract the total consumed error budget (downtime minutes) from the total allowable budget.
Remaining downtime = 5.6 minutes.
The service experienced 12 minutes of complete outage plus 4 minutes of equivalent downtime, consuming a total of 16 minutes out of the 21.6 allowable minutes.

Key Concept

Error Budget Calculation for Availability SLOs
Estimated Time:1m 30s
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Topics

Defining and Managing SLOs, SLIs, and Error Budgets

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