PCA Hard Questions — 25 Difficult Questions

Question 1

Which TWO of the following are necessary to successfully inhibit an alert in Alertmanager?

Accepted Answer

target_matchers. Inhibition requires a 'target_matchers' (the alert to be silenced) and 'source_matchers' (the alert that triggers the silence), plus common labels to correlate the two.

Answer

repeat_interval

Answer

group_wait

Answer

group_interval

Question 2

Which THREE are true regarding the Prometheus TSDB?

Accepted Answer

It uses an inverted index for fast searching.. It uses blocks, WAL, and index files, and it is optimized for time-series data.

Answer

It uses a B-tree for all queries.

Answer

It is a relational database.

Question 3

An application is emitting logs that contain '5xx' status codes when a service is unavailable. If you want to create an alert that triggers based on the rate of these errors, what is the best practice for observability?

Accepted Answer

Expose a metric incrementing on every 5xx error and alert on the rate of that metric.. Logs are useful for root cause analysis, but for alerting on rates, you should convert the error occurrence into a metric increment, as metrics are more efficient for long-term calculation and alerting.

Answer

Alert directly on the log stream using a log aggregator.

Answer

Use Prometheus to scrape the log file directly.

Answer

Increase log verbosity to trace the request until the error is resolved.

Question 4

If you are using a Histogram, what is the purpose of the '_sum' metric?

Accepted Answer

To store the sum of observations. The _sum metric provides the sum of all observed values, which allows calculating the average when combined with the _count metric.

Answer

To store the median

Answer

To store the maximum value

Answer

To store the total count

Question 5

You are seeing 'NaN' values in your gauge metrics. What does this indicate?

Accepted Answer

An undefined gauge state. NaN (Not a Number) is a valid value for gauges in Prometheus, often indicating that a value is currently undefined or not applicable.

Answer

A scrape error

Answer

Metric type mismatch

Answer

Label collision

Question 6

What does the 'resolve_timeout' setting in Alertmanager do?

Accepted Answer

It determines how long to wait before sending a resolved notification. If an alert stops firing, Alertmanager waits for the resolve_timeout duration to ensure the alert has truly resolved before notifying about the resolution.

Answer

It sets the timeout for external API calls

Answer

It defines how long to store alert history

Answer

It suppresses duplicate alerts

Question 7

You want to ensure that if the Alertmanager cluster loses communication, alerts are still sent. Which configuration helps achieve this?

Accepted Answer

Use the --cluster.peer flag. High Availability (HA) for Alertmanager is achieved by running multiple instances and using the '--cluster.peer' flag to link them.

Answer

Disable grouping

Answer

Set repeat_interval to 0

Answer

Use a load balancer only

Question 8

Which TWO of these are potential side effects of high-cardinality metrics?

Accepted Answer

High memory consumption on the Prometheus server.. Memory exhaustion (OOM) and slow query performance are the direct results of high cardinality.

Answer

Reduced CPU usage on target.

Answer

Faster alert evaluation.

Answer

Decreased network bandwidth.

Question 9

What happens if a label set for a metric changes during its lifetime?

Accepted Answer

A new time series is created. Changing a label set creates a brand new time series in Prometheus.

Answer

An error is logged

Answer

The series is updated in-place

Answer

The metric is deleted

Question 10

You are implementing a custom exporter for a legacy database. The database provides a single value representing the number of active connections. Which metric type should you use to best represent this data?

Accepted Answer

Gauge. Because active connections fluctuate up and down as users connect and disconnect, a Gauge is the appropriate metric type for representing a snapshot of the current state.

Answer

Summary

Answer

Histogram

Answer

Counter

Question 11

You need to prevent an alert from firing if a maintenance window is active. How should you approach this in Alertmanager?

Accepted Answer

Use a Silence. Silences are the standard way to prevent specific alerts from firing during a known maintenance period.

Answer

Delete the alerting rule

Answer

Modify the routing tree

Answer

Add a 'skip' label to the rule

Question 12

Which THREE of the following are valid Alertmanager routing tree parameters?

Accepted Answer

receiver. Routes can filter by 'match', 'match_re', and define a 'receiver'.

Answer

server

Answer

auth_token

Question 13

Which THREE actions are commonly performed during the 'relabeling' phase in Prometheus?

Accepted Answer

Mapping multiple labels into one.. Replacing labels, dropping series, and mapping labels are standard relabeling actions.

Answer

Configuring the storage retention policy.

Answer

Increasing the memory of the Prometheus instance.

Question 14

Your Prometheus server is hitting high memory usage due to high cardinality. Which action is most effective at reducing memory pressure?

Accepted Answer

Drop high-cardinality labels using relabel_configs. Reducing label cardinality (e.g., removing unique user IDs) is the primary way to reduce TSDB index size and memory usage.

Answer

Increase scrape_interval

Answer

Use more exporters

Answer

Enable remote write

Question 15

You are seeing 'Too many active series' in your Prometheus logs. Which action should be your first priority to address this?

Accepted Answer

Analyze the number of active series per label name.. Identifying which labels are causing the high cardinality is the standard first step to prevent OOM (Out Of Memory) crashes.

Answer

Switch to a different monitoring tool.

Answer

Disable all alerting rules.

Answer

Increase Prometheus memory limits.

Question 16

When evaluating the 'Traffic' golden signal, what is the best metric to watch for a web service?

Accepted Answer

Requests per second.. Request rate (requests per second) is the standard way to measure traffic volume.

Answer

CPU usage percentage.

Answer

HTTP error count.

Answer

Response latency.

Question 17

Which THREE factors contribute to a 'high cardinality' problem in a Prometheus environment?

Accepted Answer

Adding high-variance values like email addresses to labels.. High cardinality is caused by labels with many unique values, like timestamps, user IDs, or un-normalized request paths.

Answer

Using a low scrape interval.

Answer

Using too many scrape targets.

Question 18

Which THREE of the following fields exist in the Alertmanager 'inhibit_rules' block?

Accepted Answer

source_match. Inhibition rules require 'source_match', 'target_match', and 'equal' fields to function.

Answer

match_re

Answer

repeat

Question 19

Your application has a short-lived batch job that finishes before the Prometheus server can scrape it. What architectural component should be used?

Accepted Answer

Pushgateway. The Pushgateway is designed to allow ephemeral and batch jobs to expose their metrics to Prometheus.

Answer

Prometheus API

Answer

Alertmanager

Answer

node_exporter

Question 20

You have a histogram metric tracking request durations. You need to calculate the 99th percentile across all instances in a cluster. Why is this difficult with standard Prometheus metrics?

Accepted Answer

Aggregating histograms requires complex math because they track bucket counts, not raw values.. Histograms track counts in predefined buckets. Without knowing the exact distribution of values within those buckets, calculating accurate quantiles across multiple instances or time windows is an approximation.

Answer

Histograms can only be used on a single instance.

Answer

The Prometheus server does not support mathematical operations.

Answer

Histograms are not designed to be aggregated across multiple labels.