Monitoring with Prometheus & Grafana

You’ve built, shipped, and scaled your app. But is it healthy right now? Is it slow? About to run out of memory? Monitoring answers those questions, and it’s what separates a hobby project from a production system.

The three pillars of observability

We’ll focus on metrics, the best starting point.

Meet the dynamic duo

• Prometheus collects and stores metrics by scraping your apps at intervals.
• Grafana turns those metrics into beautiful, readable dashboards.

They’re the open-source standard for monitoring, and they pair perfectly.

How Prometheus works

1. Your app exposes metrics at an endpoint like /metrics.
2. Prometheus scrapes that endpoint every few seconds.
3. It stores the data as time series.
4. You query it with PromQL.

A metrics endpoint looks like plain text:

http_requests_total{method="GET",status="200"} 1027
process_cpu_seconds_total 4.5

Quick start with Docker Compose

services:
  prometheus:
    image: prom/prometheus
    ports:
      - "9090:9090"
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml
  grafana:
    image: grafana/grafana
    ports:
      - "3000:3000"

A minimal prometheus.yml:

global:
  scrape_interval: 15s

scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['localhost:9090']

docker compose up -d

• Prometheus UI → http://localhost:9090
• Grafana → http://localhost:3000 (default login: admin / admin)

A taste of PromQL

# Total HTTP requests
http_requests_total

# Per-second request rate over the last 5 minutes
rate(http_requests_total[5m])

# Only 500 errors
http_requests_total{status="500"}

Building a Grafana dashboard

1. In Grafana, add Prometheus as a data source (http://prometheus:9090).
2. Create a dashboard → add a panel.
3. Enter a PromQL query like rate(http_requests_total[5m]).
4. Pick a visualization (graph, gauge, stat) and save.

You can also import community dashboards by ID from grafana.com/dashboards.

Alerting

Dashboards are great, but you can’t stare at them 24/7. Set alerts to notify you (via Slack, email, PagerDuty) when something’s wrong:

“Alert me if error rate is above 5% for 5 minutes.”

Good alerts are actionable and rare. Alert fatigue, too many noisy alerts, is real, so only alert on things that need a human.

What good monitoring looks like

• Track the Four Golden Signals: latency, traffic, errors, and saturation.
• Build dashboards your whole team understands at a glance.
• Alert on symptoms users feel, not every tiny blip.

Practice challenge 🏋️

1. Spin up Prometheus + Grafana with the Compose file above.
2. Add Prometheus as a Grafana data source.
3. Build a panel showing Prometheus’s own request rate.

You did it! 🎉

That’s the full beginner DevOps journey, from “what is DevOps?” all the way to monitoring production systems. You now understand how modern software is built, shipped, run, and watched.

Keep practicing, keep building projects, and revisit the Roadmap whenever you want to go deeper. Welcome to DevOps. 🚀