Observability Examples

# Install promtool (included with Prometheus binary)
# https://prometheus.io/download/

# Validate alerting rules syntax and expressions
cd prometheus-alerts
promtool check rules orders-service.yaml

# Test alert firing logic
promtool test rules orders-service.yaml

# Request rate — is traffic flowing?
expr: rate(http_requests_total{job="orders-service"}[5m])

# Error rate — are requests succeeding?
expr: |
  rate(http_requests_total{job="orders-service",status=~"5.."}[5m])
  / rate(http_requests_total{job="orders-service"}[5m])

# Duration (p99) — how slow are requests?
expr: histogram_quantile(0.99, rate(http_request_duration_seconds_bucket{job="orders-service"}[5m]))

// Node.js — prom-client
import { Counter, Histogram } from "prom-client";

const httpRequests = new Counter({
  name: "http_requests_total",
  help: "Total HTTP requests",
  labelNames: ["method", "path", "status"],
});

const httpDuration = new Histogram({
  name: "http_request_duration_seconds",
  help: "HTTP request duration",
  labelNames: ["method", "path"],
  buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5],
});

# Python — prometheus-client
from prometheus_client import Counter, Histogram

http_requests = Counter("http_requests_total", "Total HTTP requests", ["method", "path", "status"])
http_duration = Histogram("http_request_duration_seconds", "HTTP request duration", ["method", "path"])

# Prometheus scrape config
scrape_configs:
  - job_name: orders-service
    static_configs:
      - targets: ["orders-service:9090"]