All practice questions

Question 1Question →

A mission-critical payment gateway hosted on Google Kubernetes Engine (GKE) processes $20,000,000$ valid HTTP requests over a rolling 30-day measurement window. The Site Reliability Engineering (SRE) team defines an Availability Service Level Objective (SLO) of $99.9\%$ , measured as the ratio of successful (non-HTTP 5xx) requests to total valid requests. During a bad canary release, the service logged $12,000$ HTTP 500 responses before being rolled back. No other failure events occurred during the 30-day window. What percentage of the total 30-day error budget remains after this incident?

Show answer & explanation

Answer: 40

Answer

The remaining error budget is 40.0%.

The total error budget for a 30-day period with

20,000,000

requests at a

99.9\%

SLO target is

20,000,000 \times 0.001 = 20,000

allowable failed requests. The incident consumed

12,000

requests (

60\%

of the budget). Therefore,

20,000 - 12,000 = 8,000

allowed failed requests remain, which represents

(8,000 / 20,000) \times 100 = 40.0\%

of the original error budget.

Step-by-Step Solution

1

Calculate the total allowable error budget (in number of failed requests) from the SLO target.

Total Error Budget =

20,000,000 \times (1 - 0.999) = 20,000

requests.

An Availability SLO of

99.9\%

allows an error rate of

0.1\%

(

0.001

) across all incoming valid requests.

2

Subtract the consumed bad requests from the total allowable error budget.

Remaining Error Budget (in requests) =

20,000 - 12,000 = 8,000

requests.

The canary incident consumed

12,000

failed requests out of the

20,000

total allowed budget.

3

Calculate the percentage of the error budget remaining relative to the original error budget.

Remaining Percentage =

(8,000 / 20,000) \times 100 = 40.0\%

.

Error budget remaining is expressed as a fraction of the total allowable error budget, not the total request volume.

Key Concept

Error Budget Calculation based on Request-Based SLIs and SLO targets

Question 2Question →

A cloud architecture team defines a Service Level Objective (SLO) for an enterprise user authentication API hosted on Google Cloud. The team sets an availability SLO target of $99.9\%$ measured over a rolling period of 30 days ( $43,200$ minutes). What is the maximum total downtime in minutes allowed before the service completely exhausts its error budget for this 30-day period?

Show answer & explanation

Answer: 43.2

Answer

The maximum allowable downtime before completely exhausting the 30-day error budget is

43.2

minutes.

An availability SLO target of

99.9\%

permits an error budget of

0.1\%

(

100\% - 99.9\%

). Across a 30-day window (

43,200

minutes), the maximum allowable downtime in minutes is

43,200 \times 0.001 = 43.2

minutes.

Step-by-Step Solution

1

Determine the error budget percentage allowed by the SLO

0.1\%

or

0.001

of total operational time

The error budget represents the allowable failure rate, calculated as

100\% - \text{SLO}

(

100\% - 99.9\% = 0.1\%

).

2

Calculate total allowable downtime in minutes over the 30-day measurement window

43.2

minutes

Multiply total minutes in 30 days (

43,200

minutes) by the error budget fraction (

0.001

):

43,200 \times 0.001 = 43.2

minutes.

Key Concept

Error Budget Downtime Calculation

Question 3Question →

An enterprise payment processing service hosted on Google Cloud Platform has a defined Service Level Objective (SLO) of $99.95\%$ availability for its transaction validation API over a $30$ -day rolling period. The Service Level Indicator (SLI) evaluates a request as good if it returns an HTTP $200\text{ OK}$ status code in under $500\text{ ms}$ .

During a $30$ -day window, the service processes a total of $8,000,000$ requests. Due to a database failover event, $1,800$ requests fail with HTTP $500$ internal server errors. Additionally, $600$ requests successfully return HTTP $200$ but take longer than $500\text{ ms}$ to complete.

What is the maximum number of additional non-compliant requests the service can sustain before its total error budget for this $30$ -day period is completely exhausted?

Show answer & explanation

Answer: 1600

Answer

1,600 requests

The total error budget is calculated as

0.05\%

of

8,000,000

total requests, which equals

4,000

allowable non-compliant requests. Subtracting the

1,800

HTTP 500 errors and

600

latency threshold breaches (totaling

2,400

bad requests) leaves exactly

1,600

remaining requests in the error budget.

Step-by-Step Solution

1

Calculate the total error budget allowance in terms of total non-compliant requests for the 30-day window

Total Error Budget =

8,000,000 \times (100\% - 99.95\%) = 8,000,000 \times 0.0005 = 4,000

requests.

An SLO of

99.95\%

target success rate allows a failure rate of

0.05\%

across all incoming requests within the evaluation window.

2

Determine the total consumed error budget by summing all bad requests according to the defined SLI criteria

Consumed Budget =

1,800\text{ (explicit HTTP 500 errors)} + 600\text{ (latency breaches above } 500\text{ ms)} = 2,400

non-compliant requests.

The SLI specifies that both HTTP errors and requests exceeding the

500\text{ ms}

latency threshold count against the service reliability budget.

3

Calculate the remaining allowable non-compliant requests

Remaining Error Budget =

4,000 - 2,400 = 1,600

requests.

Subtracting the already consumed error budget from the initial total budget yields the remaining buffer before SLO violation occurs.

Key Concept

Calculating Error Budget Consumption using Request-based SLIs

Question 4Question →

A healthcare telemetry platform hosted on Google Cloud Run and Cloud Bigtable processes real-time patient metrics. The Site Reliability Engineering (SRE) team defines an availability Service Level Objective (SLO) of $99.9\%$ measured over a rolling 30-day window ( $43,200$ minutes). During an unexpected deployment failure, the service suffered complete downtime for $18$ minutes. Later in the same rolling window, a database connection pool exhaustion caused a partial degradation for $60$ minutes, during which $40\%$ of all incoming telemetry requests failed. Assuming a constant request rate throughout the window, how many minutes of error budget remain for this 30-day period?

Show answer & explanation

Answer: 1.2

Answer

The remaining error budget for the rolling 30-day window is

1.2

minutes.

For a 30-day window (

43,200

minutes) with a

99.9\%

SLO target, the total allowable error budget is

0.1\% \times 43,200 = 43.2

minutes. The complete outage consumed

18

minutes. The partial degradation consumed

60 \times 0.40 = 24

minutes of equivalent downtime budget. Total consumed error budget is

18 + 24 = 42

minutes. Therefore, the remaining error budget is

43.2 - 42 = 1.2

minutes.

Step-by-Step Solution

1

Calculate the total allowable error budget in minutes for the 30-day window

Total error budget =

43,200 \text{ minutes} \times (1 - 0.999) = 43.2 \text{ minutes}

.

An SLO of

99.9\%

allows for an unreliability margin (error budget) of

0.1\%

(

0.001

) over the

43,200

-minute window.

2

Determine error budget consumed during the full outage

Full outage budget consumed =

18 \text{ minutes} \times 100\% = 18.0 \text{ minutes}

.

During complete downtime (

100\%

request failure rate), every minute counts fully against the error budget.

3

Determine error budget consumed during the partial degradation

Partial outage budget consumed =

60 \text{ minutes} \times 40\% = 24.0 \text{ minutes}

.

Under constant traffic conditions, partial failures consume error budget proportionally to the error rate (

60 \times 0.40 = 24.0

minutes).

4

Calculate total consumed error budget and remaining budget

Total consumed =

18.0 + 24.0 = 42.0 \text{ minutes}

. Remaining error budget =

43.2 - 42.0 = 1.2 \text{ minutes}

.

Subtracting the total consumed downtime equivalent (

42.0

minutes) from the allowable budget (

43.2

minutes) yields the remaining error budget.

Key Concept

Error Budget Calculation for Service Level Objectives

Estimated Time:2m 0s

Question 5Question →

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 $99.95\%$ 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?

Show answer & explanation

Answer: 5.6

Answer

The remaining allowable downtime is 5.6 minutes.

For a 30-day window, total minutes equal

30 \times 24 \times 60 = 43,200

minutes. With an SLO of

99.95\%

, the allowable downtime percentage is

0.05\%

, giving a maximum allowable downtime of

43,200 \times 0.0005 = 21.6

minutes. Since

16

minutes (

12 + 4

) of error budget have already been consumed, the remaining allowable downtime is

21.6 - 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

Question 6Question →

A real-time payment reconciliation API deployed on Google Kubernetes Engine (GKE) has a Service Level Objective (SLO) of $99.9\%$ successful requests measured over a $30$ -day rolling window. During a given $30$ -day period, the API receives a total of $80,000,000$ valid requests. What is the maximum number of failed requests allowed during this period before the service exhausts its error budget?

Show answer & explanation

Answer: 80000

Answer

The maximum number of allowed failed requests before exhausting the error budget is 80,000 requests.

The error budget represents the fraction of bad requests tolerated while maintaining the defined SLO. For a

99.9\%

target across

80,000,000

total requests, the allowable error rate is

0.1\%

(

0.001

). Multiplying

80,000,000

requests by

0.001

yields exactly

80,000

allowed failed requests.

Step-by-Step Solution

1

Calculate the allowable failure rate

Failure rate =

1 - 0.999 = 0.001

(

0.1\%

)

The error budget is the inverse of the target Service Level Objective (SLO).

2

Calculate the absolute error budget in number of requests

Error Budget =

80,000,000 \times 0.001 = 80,000

requests

Applying the failure rate fraction to the total request volume yields the total count of failed requests tolerated within the SLO window.

Key Concept

Calculating Request-Based Error Budgets for SLO Management

Question 7Question →

An enterprise healthcare provider operates an electronic health records (EHR) API Gateway on Google Cloud with a defined Service Level Objective (SLO) of $99.9\%$ availability over a rolling $30$ -day window ( $43,200$ minutes). Over the current $30$ -day window, the service experienced two incidents while maintaining constant request volume: a database outage resulted in a complete service failure ( $100\%$ error rate) lasting $15$ minutes, and a downstream service throttling issue resulted in a partial degradation ( $40\%$ error rate) lasting $45$ minutes. What is the remaining allowable error budget in minutes for this $30$ -day window?

Show answer & explanation

Answer: 10.2

Answer

The remaining allowable error budget for the 30-day window is 10.2 minutes.

The total allowable error budget for a 99.9% SLO over 30 days (43,200 minutes) is

0.001 \times 43,200 = 43.2

minutes. Incident 1 (100% failure for 15 minutes) consumes 15.0 minutes. Incident 2 (40% failure for 45 minutes under uniform traffic) consumes

45 \times 0.40 = 18.0

minutes. Total consumed budget is

15.0 + 18.0 = 33.0

minutes. Subtracting the consumed budget from the total allowable budget leaves

43.2 - 33.0 = 10.2

minutes.

Step-by-Step Solution

1

Calculate the total allowable error budget for a 99.9% availability SLO over 30 days (43,200 minutes).

Total Error Budget =

43,200 \times (1 - 0.999) = 43.2

minutes.

An SLO of 99.9% permits a maximum error rate of 0.1% across the entire rolling window.

2

Compute the effective downtime minutes consumed during the total outage incident.

Incident 1 Budget Consumed =

15 \text{ minutes} \times 100\% = 15.0

minutes.

A 100% error rate for 15 minutes consumes 15 full minutes of error budget.

3

Compute the effective downtime minutes consumed during the degraded state incident.

Incident 2 Budget Consumed =

45 \text{ minutes} \times 40\% = 18.0

minutes.

Under uniform traffic, a partial outage with a 40% error rate for 45 minutes consumes equivalent error budget proportional to the failure fraction (

45 \times 0.40

).

4

Sum the error budget consumed across both operational incidents.

Total Consumed =

15.0 + 18.0 = 33.0

minutes.

Combining the impact of full and partial outages gives the total budget spent.

5

Subtract total consumed budget from total allowable budget.

Remaining Error Budget =

43.2 - 33.0 = 10.2

minutes.

This yields the remaining margin of unreliability permitted before breaching the SLO target.

Key Concept

SLO Error Budget Calculation for Partial and Total Outages

Question 8Question →

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 $99.95\%$ successful requests (HTTP non-5xx status codes) over a rolling 30-day measurement window. During a period where the service processed exactly $40,000,000$ total requests, an infrastructure outage caused $12,000$ request failures. How many additional failed requests can the API tolerate during this measurement window before completely exhausting its error budget?

Show answer & explanation

Answer: 8000

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\%

on

40,000,000

requests, the total error budget is

40,000,000 \times (1 - 0.9995) = 20,000

allowed error requests. Having already incurred

12,000

errors, the remaining error budget is

20,000 - 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 \times (1 - 0.9995) = 20,000

failed requests.

An availability SLO of

99.95\%

allows an unreliability budget of

0.05\%

(or

0.0005

) of total requests.

2

Calculate the remaining allowable error budget.

Remaining error budget =

20,000 - 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

Answer

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