PCA: Prometheus Certified Associate

In PromQL, offset shifts an instant-vector selector back in time and must immediately follow that selector. Thus, node_memory_MemAvailable_bytes offset 10m retrieves the values from 10 minutes ago, and sum(...) totals them across all matching series.

PromQL’s month() function returns the calendar month, in UTC, for each input timestamp. Applying it to prometheus_tsdb_lowest_timestamp_seconds extracts the month represented by that metric’s Unix timestamp.

The @ modifier must immediately follow an instant-vector or range-vector selector. It cannot be applied to the result of sum(...); the timestamp modifier belongs inside the aggregation, attached to http_requests_total{method="GET"}. start() and end() are valid special values for this modifier.

A summary or classic histogram exposes the cumulative sum of observed durations as http_request_duration_seconds_sum and the number of observations as http_request_duration_seconds_count. Dividing the five-minute rate of the sum by the five-minute rate of the count yields the average request duration during that interval.

Prometheus naming conventions recommend base units and a plural unit suffix. Response size is measured in bytes, so the metric name should use the _bytes suffix; _total is reserved for accumulating counters.