The observability stack finally lands on obs-01, and its first working tool is Prometheus. This chapter covers the server end to end — the pull model, prometheus.yml, the exporters that translate hosts and stores, service discovery and relabeling, the TSDB on disk, and the scaling ladder — and finishes with the first real telemetry Harborline has ever had: six hosts and three stores reporting every 15 seconds.
6 topics
One docker compose up on obs-01 brings up Prometheus, Grafana, Loki, Tempo, and Alertmanager — but only Prometheus does real work this chapter. node_exporter goes onto all six machines, postgres_exporter onto db-01, redis_exporter onto cache-01, and RabbitMQ's built-in plugin switches on for mq-01. By the last topic, Mara has host- and store-level telemetry for the whole fleet. The five services themselves stay dark; instrumenting them is Chapter 5's job.
Six topics take the server apart: the pull-model architecture and the deliberate list of things Prometheus refuses to do; the one YAML file that declares everything; the exporter ecosystem that translates systems that don't speak Prometheus; service discovery and the relabeling rule language that shapes every target; the TSDB's head-WAL-and-blocks design with its one-line sizing arithmetic; and the scaling ladder, climbed only as far as honesty requires.
The scrape topology — obs-01 pulls /metrics from every target
Prometheus on obs-01 initiates every scrape; targets never push