Linux Foundation PCA Exam Questions

The metric user_last_login_timestamp_seconds{email='john.doe@example.com'} is unsuitable for Prometheus because it includes a high-cardinality label (email). Each unique email address would generate a separate time series, potentially numbering in the millions, which severely impacts Prometheus performance and memory usage.

Prometheus is optimized for low- to medium-cardinality metrics that represent system-wide behavior rather than per-user data. High-cardinality metrics cause data explosion, complicating queries and overwhelming the storage engine.

By contrast, the other metrics---prometheus_engine_query_log_enabled, promhttp_metric_handler_requests_total{code='500'}, and http_response_total{handler='static/*filepath'}---adhere to Prometheus best practices. They represent operational or service-level metrics with limited, manageable label value sets.

Extracted and verified from Prometheus documentation -- Metric and Label Naming Best Practices, Cardinality Management, and Anti-Patterns for Metric Design sections.

In PromQL, the offset modifier allows you to query metrics as they were at a past time relative to the current evaluation. To retrieve the value of node_memory_MemAvailable_bytes as it was 10 minutes ago, you place the offset keyword inside the aggregation function's argument, not after it.

The correct query is:

sum(node_memory_MemAvailable_bytes offset 10m)

This computes the total available memory across all instances, based on data from exactly 10 minutes in the past.

Placing offset after the aggregation (as in option B) is syntactically invalid because modifiers apply to instant and range vector selectors, not to complete expressions.

Verified from Prometheus documentation -- PromQL Evaluation Modifiers: offset, Aggregation Operators, and Temporal Query Examples.

According to Prometheus naming rules, metric names must match the regex [a-zA-Z_:][a-zA-Z0-9_:]*. This means metric names must begin with a letter, underscore, or colon, and can only contain letters, digits, and underscores thereafter.

The valid metric name among the options is go_goroutines, which follows all these rules. It starts with a letter (g), uses underscores to separate words, and contains only allowed characters.

By contrast:

go routines is invalid because it contains a space.

go.goroutines is invalid because it contains a dot (.), which is reserved for recording rule naming hierarchies, not metric identifiers.

99_goroutines is invalid because metric names cannot start with a number.

Following these conventions ensures compatibility with PromQL syntax and Prometheus' internal data model.

Extracted from Prometheus documentation -- Metric Naming Conventions and Data Model Rules sections.

Prometheus collects metrics by scraping an HTTP endpoint exposed by the target application. Therefore, the only essential requirement for an application to expose metrics to Prometheus is that it serves metrics in the Prometheus text exposition format over HTTP.

This endpoint is conventionally available at /metrics and provides metrics in plain text format (e.g., Content-Type: text/plain; version=0.0.4). The application can run on any operating system, architecture, or network --- as long as Prometheus can reach its endpoint.

It does not need to be Internet-accessible (it can be internal) and is not limited to Linux or any specific bitness.

Verified from Prometheus documentation -- Exposition Formats, Instrumenting Applications, and Target Scraping Requirements sections.

The official Prometheus exporter for collecting system-level and kernel-related metrics from Linux and other UNIX-like operating systems is the Node Exporter.

The Node Exporter exposes hardware and OS metrics including CPU load, memory usage, disk I/O, network traffic, and kernel statistics. It is designed to provide host-level observability and serves data at the default endpoint :9100/metrics in the standard Prometheus exposition text format.

This exporter is part of the official Prometheus ecosystem and is widely deployed for infrastructure monitoring. None of the other listed options (Prometheus_exporter, metrics_exporter, or os_exporter) are official components of the Prometheus project.

Verified from Prometheus documentation -- Node Exporter Overview, System Metrics Collection, and Official Exporters List.