PCDE Applying Site Reliability Engineering Practices to a Service — 40 Questions

Question 1

An SRE team wants to define an SLI for service availability. Which metric correctly represents the availability SLI?

Accepted Answer

Total requests that succeed / Total requests. Availability as an SLI is measured as the proportion of successful requests to total requests. Option A correctly defines this as 'Total requests that succeed / Total requests'. Option B is incorrect because it measures latency (response time within 200 ms), not availability. Option C is a measure of uptime, not service availability from the user's perspective. Option D only counts errors, which is not a ratio.

Answer

Total requests that complete within 200 ms / Total requests

Answer

Total minutes the service is up / Total minutes in the window

Answer

Number of requests that return a 5xx status code

Question 2

A service has an SLO of 99.9% availability over a 30-day month. What is the error budget in minutes for that month?

Accepted Answer

43.2 minutes. Error budget = (100% - SLO) * total time. 0.1% of 43,200 minutes (30 days) is 43.2 minutes. Rounded to 43 minutes.

Answer

144 minutes

Answer

4.32 minutes

Answer

432 minutes

Question 3

An engineer needs to set up alerting for error budget burn rate. For a fast burn alert, which burn rate multiplier and evaluation window are recommended?

Accepted Answer

1-hour window, 14x burn rate. Fast burn alert uses a 1-hour window and 14x burn rate. Slow burn uses 6-hour window and 5x burn rate.

Answer

6-hour window, 5x burn rate

Answer

1-hour window, 5x burn rate

Answer

6-hour window, 14x burn rate

Question 4

A team wants to reduce toil by automating a manual process that generates a report from Cloud Logging logs and emails it weekly. Which solution is most cost-effective and requires minimal operational overhead?

Accepted Answer

Cloud Scheduler + Cloud Functions. Cloud Scheduler triggers a Cloud Function or runs a query in BigQuery, but the most straightforward serverless option is a Cloud Function triggered by Cloud Scheduler. Cloud Composer is heavy for a simple report. Cloud Run requires containerization. Cloud Build is for CI/CD.

Answer

Cloud Run job manually started

Answer

Cloud Build trigger on schedule

Answer

Cloud Composer (Airflow) DAG

Question 5

During an incident, the incident commander identifies a need to scale up a managed instance group. Which IAM role should be granted to the on-call engineer to allow them to modify the instance group?

Accepted Answer

roles/compute.instanceAdmin.v1. Compute Instance Admin (roles/compute.instanceAdmin.v1) allows full control over instances and instance groups, including modifying MIGs. Instance Admin (basic) is restricted. Compute Admin is broader but includes other resources. Security Admin does not have compute permissions.

Answer

roles/compute.admin

Answer

roles/compute.securityAdmin

Answer

roles/compute.instanceAdmin (basic)

Question 6

A service has an SLO based on request latency: 99% of requests must complete under 500ms over a 28-day window. The team wants to monitor the error budget burn rate. Which Cloud Monitoring SLO type and configuration should be used?

Accepted Answer

Request-based SLO: good request count / valid request count with threshold 500ms. A request-based SLO with a good-request-count/valid-request-count metric is appropriate for latency SLIs. The threshold is set at 500ms. Window-based SLOs are for uptime, not latency.

Answer

Window-based SLO: good minutes / total minutes with threshold 500ms

Answer

Request-based SLO: good request count / total request count with threshold 500ms

Answer

Window-based SLO: good requests / total requests with threshold 500ms

Question 7

Which of the following best describes 'toil' in SRE?

Accepted Answer

Manual, repetitive work that provides no enduring value and scales linearly with service growth. Toil is work that is manual, repetitive, automatable, and does not provide enduring value. It scales with service growth.

Answer

Work that is creative and requires deep domain knowledge

Answer

Automating infrastructure provisioning

Answer

Incident response and on-call duties

Question 8

A team wants to implement chaos engineering on Google Kubernetes Engine (GKE) to test resilience against pod failures. Which tool is designed for injecting faults into GKE clusters?

Accepted Answer

Chaos Mesh on GKE. Chaos Mesh is an open-source chaos engineering platform for Kubernetes, including GKE. It can inject pod failures, network delays, etc. Traffic Director fault injection is for service mesh, not GKE-native.

Answer

GKE Node Auto-Repair

Answer

Traffic Director fault injection

Answer

Cloud Armor

Question 9

An SRE team uses Cloud Monitoring SLOs with an error budget policy. They want to receive an alert when the error budget is exhausted at a rate that would exhaust it in 1 hour (fast burn). The SLO is 99.9% over 30 days. The error budget is 43.2 minutes. What burn rate threshold should be used?

Accepted Answer

14. In Google SRE practice, a fast burn alert uses a 1-hour window and a burn rate threshold of 14. This means the alert fires when the error rate exceeds 14 times the allowable rate, indicating that the budget is being consumed rapidly. At a burn rate of 14, the budget would be exhausted in 30 days / 14 ≈ 2.14 days. The question's reference to 'exhaust it in 1 hour' refers to the alert's lookback window (1 hour), not the actual time to budget exhaustion. A burn rate of 720 would exhaust the budget in 1 hour, but that is not a standard alert threshold. Therefore, the correct answer is 14.

Answer

5

Answer

720

Answer

1

Question 10

During a blameless postmortem, the team uses the '5 Whys' technique to identify root causes. What is the primary purpose of this technique?

Accepted Answer

To iteratively ask 'why' to uncover the root cause. 5 Whys is a root cause analysis technique used to uncover the underlying causes of an incident, not to assign blame or find contributors superficially.

Answer

To estimate the cost of the incident

Answer

To identify the immediate superficial cause of the incident

Answer

To determine which team member made an error

Question 11

A company wants to implement a service mesh with fault injection for HTTP services running on Google Kubernetes Engine. They need to inject artificial delays and errors into requests to test resilience. Which GCP service should they use?

Accepted Answer

Traffic Director. Traffic Director is a managed traffic control plane that supports HTTP fault injection via the HTTP fault filter. It integrates with GKE ingress.

Answer

Cloud Armor

Answer

Cloud Load Balancing

Answer

Cloud Endpoints

Question 12

An SRE team defines an SLO for a batch processing pipeline. Which SLI is most appropriate for pipeline freshness?

Accepted Answer

Age of the most recent output record. Pipeline freshness measures how up-to-date the output data is compared to the input. It's best measured by the age of the most recent output record.

Answer

Percentage of records with correct values

Answer

Number of records processed per second

Answer

Number of failed pipeline runs

Question 13

Which TWO components are essential for setting up an incident management on-call rotation in Google Cloud? (Choose 2)

Accepted Answer

Cloud Monitoring alert notification channels. Cloud Monitoring alert notification channels are used to route alerts to on-call tools like PagerDuty or OpsGenie. An on-call schedule defines who is on call. The other options are not directly related.

Answer

Cloud Build trigger for incidents

Answer

Cloud Functions to handle alerts

Answer

Traffic Director routing rules

Question 14

Which THREE are key principles of a blameless postmortem culture in SRE? (Choose 3)

Accepted Answer

Creating action items with owners and due dates. Blameless postmortems focus on systemic improvements, not individual blame. They involve documenting contributing factors, creating action items with owners and dates, and fostering a culture of learning. Assigning blame is avoided.

Answer

Ensuring incidents are never discussed outside the team

Answer

Assigning responsibility to individuals for errors

Question 15

Which TWO metrics are appropriate for defining a request-based SLI for a web service? (Choose 2)

Accepted Answer

Latency: proportion of requests under a threshold. Request-based SLIs include availability (successful/total) and latency (proportion under threshold). Throughput and error count are not SLIs themselves but can be used in SLO definitions. Uptime is a window-based metric.

Answer

Throughput: requests per second

Answer

Error count: number of 5xx responses

Answer

Uptime: minutes service is up

Question 16

A site reliability engineer is defining an SLO for a service that processes user uploads. The team wants to measure success as the proportion of uploads completed within 2 seconds. Which type of SLI should they use?

Accepted Answer

Latency-based SLI measuring proportion of requests under a threshold. This scenario describes a request-based SLI where each upload is a request, and success is defined by latency being under a threshold (2 seconds). Request-based SLIs count good requests (those meeting the criteria) over total requests.

Answer

Throughput-based SLI measuring requests per second

Answer

Freshness-based SLI measuring time since last successful upload

Answer

Availability-based SLI using successful/total requests

Question 17

A team's SLO for availability is 99.9% over a 30-day window. They have consumed 80% of their error budget halfway through the month. What is the remaining allowed downtime for the rest of the month?

Accepted Answer

About 8 minutes 38 seconds. Total error budget = 100% - 99.9% = 0.1% of 30 days = 43.2 minutes (0.1% * 30 * 1440). 80% consumed means 20% remains: 0.2 * 43.2 = 8.64 minutes, approximately 8 minutes 38 seconds.

Answer

About 17 minutes 17 seconds

Answer

About 34 minutes 34 seconds

Answer

About 43 minutes 12 seconds

Question 18

You are configuring error budget burn rate alerts for an SLO with a 30-day window. The SLO target is 99.9%. You want to alert if the error budget is projected to be fully consumed in 2 hours, using a fast burn rate. Which alerting policy configuration should you use?

Accepted Answer

Burn rate threshold: 14, lookback window: 1 hour. Fast burn alert: burn rate > 14x for 1-hour window. If full budget consumed in 2 hours, burn rate = (30 days * 1440 min/day) / (2 hours * 60 min/hour) = 43200 / 120 = 360. But the standard fast burn alert uses a 1-hour window and a burn rate threshold of 14, which corresponds to consuming the budget in ~2 hours (43200/14 ≈ 3085 min ≈ 2.14 days). To alert on 2-hour consumption, you need a custom alert with a burn rate of 14 and a lookback window of 1 hour (the standard fast burn configuration). That alert triggers when the rate of budget consumption would exhaust the budget in ~2 hours if sustained.

Answer

Burn rate threshold: 14, lookback window: 6 hours

Answer

Burn rate threshold: 5, lookback window: 1 hour

Answer

Burn rate threshold: 5, lookback window: 6 hours

Question 19

An SRE team wants to reduce toil associated with manual database schema migrations. They currently run SQL scripts manually during maintenance windows. Which Google Cloud service is most appropriate to automate this process in a repeatable way?

Accepted Answer

Cloud Build. Cloud Build is a CI/CD platform that can execute SQL migration scripts as part of a build pipeline. It integrates with Cloud Source Repositories and can trigger on schema changes. Cloud Functions and Workflows are more for event-driven workflows, not typical for database migrations.

Answer

Cloud Scheduler

Answer

Workflows

Answer

Cloud Functions

Question 20

During a blameless postmortem after an incident, the team identified that the root cause was a misconfigured load balancer health check. Which practice should the team prioritize to prevent recurrence?

Accepted Answer

Add a test in CI/CD to validate health check configuration. A blameless postmortem focuses on finding contributing factors and creating action items to improve the system. The action item should be to fix the health check configuration and automate validation. Implementing a runbook for future incidents is reactive, not preventive. Creating a rollback plan is also reactive.

Answer

Create a rollback plan for health check changes

Answer

Schedule a weekly manual review of load balancer settings

Answer

Write a runbook for future load balancer incidents