What Is a Metric, in Monitoring Terms?
A ground-up tour of the numeric “measurements over time” that power every green graph and red alert — counters, gauges, histograms, and summaries; push vs pull collection; the five-layer metrics pipeline; JWT-style time-series storage in a TSDB; cardinality discipline, downsampling, write-ahead logs; the four golden signals, RED, USE, SLIs/SLOs/error budgets;…