Prometheus Architecture Deep Dive

Calendar February 22, 2026
Observability
Intermediate
Prometheus-Architecture, Scrape-Configuration, Service-Discovery-Setup, Long-Term-Storage-Design
Prometheus, Tsdb, Service-Discovery, Relabeling, Federation, Remote-Write, Thanos, Mimir
Prometheus, Thanos, Mimir, Cortex, Consul

Pull-Based Scraping Model#

Prometheus pulls metrics from targets rather than having targets push metrics to it. Every scrape interval (default 15s in the global config), Prometheus sends an HTTP GET to each target’s metrics endpoint. The target responds with all its current metric values in Prometheus exposition format.

This pull model has concrete advantages. Prometheus controls the scrape rate, so a misbehaving target cannot flood the system. You can scrape a target from your laptop with curl http://target:8080/metrics to see exactly what Prometheus sees. Targets that go down are immediately detectable because the scrape fails.

Prometheus Cardinality Management: Detecting, Preventing, and Reducing High-Cardinality Metrics

Calendar February 21, 2026
Observability
Advanced
Cardinality-Analysis, Metric-Relabeling, Recording-Rule-Design, Prometheus-Performance-Tuning
Prometheus, Cardinality, Time-Series, Relabeling, Recording-Rules, Performance, Tsdb, Labels
Prometheus, Grafana, Promtool

What Cardinality Means#

In Prometheus, cardinality is the number of unique time series. Every unique combination of metric name and label key-value pairs constitutes one series. The metric http_requests_total{method="GET", path="/api/users", status="200"} is one series. Change any label value and you get a different series. http_requests_total{method="POST", path="/api/users", status="201"} is a second series.

A single metric name can produce thousands or millions of series depending on its labels. A metric with no labels is exactly one series. A metric with one label that has 10 possible values is 10 series. A metric with three labels, each having 100 possible values, is up to 1,000,000 series (100 x 100 x 100), though in practice not every combination occurs.