Important Linux Foundation PCA Exam Questions

Answer: A

Explanation:

In Prometheus best practices, high-cardinality labels---especially those containing unique or user-specific identifiers---should be avoided. The metric myapp_filG_uploads_total{userid='5123',status='failed'} exposes the userid as a label, which is problematic. Each distinct value of a label generates a new time series in Prometheus. If there are thousands or millions of unique users, this would exponentially increase the number of time series, leading to cardinality explosion, degraded performance, and high memory usage.

The _total suffix is actually correct and required for counters, as per the Prometheus naming convention. The use of underscores in metric names is also correct, as Prometheus does not support dashes in metric identifiers. The status label, however, is perfectly valid because it typically has a low number of possible values (e.g., ''success'', ''failed'').

Verified from Prometheus official documentation sections Instrumentation -- Metric and Label Naming Best Practices and Writing Exporters.

Answer: B

Explanation:

The increase() function computes the total increase in a counter metric over a specified range vector. It accounts for counter resets and only measures the net change in the counter's value during the time window.

Example:

increase(http_requests_total[5m])

This query returns how many HTTP requests occurred in the last five minutes. Unlike rate(), which provides a per-second average rate, increase() gives the absolute number of increments.

Answer: B

Explanation:

By default, Prometheus stores its time series data in a local, embedded Time Series Database (TSDB) on disk. The data is organized in block files under the data/ directory inside Prometheus's storage path.

Each block typically covers two hours of data, containing chunks, index, and metadata files. Older blocks are compacted and deleted based on retention settings.

Answer: B

Explanation:

The Pushgateway is a Prometheus component used to handle short-lived batch jobs that cannot be scraped directly. These jobs push their metrics to the Pushgateway, which then exposes them for Prometheus to scrape.

This ensures metrics persist beyond the job's lifetime. However, it's not designed for continuously running services, as metrics in the Pushgateway remain static until replaced.

Answer: D

Explanation:

In Prometheus alerting rules, the for field specifies how long a condition must remain true continuously before the alert transitions from the pending to the firing state. This feature prevents transient spikes or brief metric fluctuations from triggering false alerts.

Example:

alert: HighRequestLatency

expr: http_request_duration_seconds_avg > 1

for: 5m

labels:

severity: warning

annotations:

description: 'Request latency is above 1s for more than 5 minutes.'

In this configuration, Prometheus evaluates the expression every rule evaluation cycle. The alert only fires if the condition (http_request_duration_seconds_avg > 1) remains true for 5 consecutive minutes. If it returns to normal before that duration, the alert resets and never fires.

This mechanism adds stability and noise reduction to alerting systems by ensuring only sustained issues generate notifications.

Verified from Prometheus documentation -- Alerting Rules Configuration Syntax, Pending vs. Firing States, and Best Practices for Alert Timing and Thresholds sections.