Connect bounded RED metrics and SLOs to one question

Observability answers incident questions; it is not a contest to store the most data. Collect Rate, Errors, and Duration by route template, then connect logs and asynchronous work with request context.

Never use the raw 404 path as a metric label: bots can create unbounded time series. Python backend folds unmatched routes into /_not_found. User IDs, filenames, and search terms must not become labels either.

Java dmddksl/da2ari expose Actuator Prometheus endpoints and Python exposes standard /metrics. Compose Prometheus scrapes them only in the optional profile. Grafana and a Next.js-specific exporter are not installed because the runtimes and deployment platforms do not yet share an operations contract; Next.js keeps logs, Sentry, and Web Vitals.

Define an SLO from a user path and baseline. If there is no measurement, do not promise an arbitrary 99.9%; agree on error-budget, deployment-pause, and rollback actions after collecting the baseline.

Related course: RED, correlation, and SLOs