What is the difference between Prometheus and Grafana?
Understand the difference between Prometheus and Grafana: Prometheus stores metrics, Grafana visualizes them. Learn how they work together in monitoring.
Expected Interview Answer
Prometheus is a time-series database and monitoring system that collects and stores metrics and evaluates alerting rules, while Grafana is a visualization and dashboarding tool that queries those metrics and displays them as graphs.
Prometheus scrapes metrics from targets, stores them with labels, exposes the PromQL query language, and fires alerts through Alertmanager. Grafana does not collect or store metrics itself; it connects to data sources like Prometheus (and many others) and turns their query results into dashboards, panels, and alerts. In practice they are complementary: Prometheus is the data engine, Grafana is the presentation layer.
- Clear separation of collection vs visualization
- Grafana supports many data sources, not just Prometheus
- Prometheus provides pull-based scraping and PromQL
- Together they form a complete observability stack
- Each can be scaled and operated independently
AI Mentor Explanation
Prometheus is like the official scorer who records every ball, run, and wicket into the scorebook throughout the match. Grafana is the giant stadium scoreboard and TV graphics that read from that record and show run-rate charts and worm graphs. The scorer captures and stores the raw data; the display only presents what the scorer already logged.
Step-by-Step Explanation
Step 1
Prometheus collects
Prometheus scrapes metrics endpoints on a schedule and stores them as labeled time series.
Step 2
Prometheus queries and alerts
PromQL evaluates the stored series for dashboards and alerting rules routed via Alertmanager.
Step 3
Grafana connects
Grafana is configured with Prometheus as a data source using its HTTP query API.
Step 4
Grafana visualizes
Grafana runs PromQL queries and renders the results into panels, dashboards, and alerts.
Step 5
They combine
Prometheus is the storage and query engine; Grafana is the visualization layer on top.
What Interviewer Expects
- Prometheus stores metrics, Grafana does not
- Grafana supports multiple data sources
- Understanding of PromQL as the query bridge
- Awareness that both can do alerting
- Recognition that they are complementary, not competing
Common Mistakes
- Saying Grafana stores or collects metrics
- Claiming you must choose one over the other
- Thinking Grafana only works with Prometheus
- Confusing dashboards with the underlying data engine
Best Answer (HR Friendly)
“Prometheus is the tool that collects and stores your system's performance numbers, and Grafana is the tool that turns those numbers into readable charts and dashboards. You typically use them together: Prometheus gathers the data, Grafana displays it.”
Code Example
apiVersion: 1
datasources:
- name: Prometheus
type: prometheus
access: proxy
url: http://prometheus:9090
isDefault: trueFollow-up Questions
- How does Grafana query Prometheus under the hood?
- Can Prometheus create dashboards on its own?
- What other data sources can Grafana connect to?
- Where does Alertmanager fit into this stack?
- How would you scale Prometheus storage long term?
MCQ Practice
1. Which component actually stores the time-series metrics?
Prometheus stores metrics as labeled time series; Grafana only queries and visualizes them.
2. What is Grafana's primary role?
Grafana is a visualization layer that reads from data sources and renders dashboards and panels.
3. How does Grafana get data from Prometheus?
Grafana issues PromQL queries against Prometheus's HTTP query API and charts the results.
Flash Cards
What does Prometheus do? — Scrapes, stores, and queries time-series metrics and evaluates alert rules.
What does Grafana do? — Connects to data sources and visualizes their metrics as dashboards and panels.
Does Grafana store metrics? — No. It is stateless for metrics and reads from data sources like Prometheus.
Are they competitors? — No, they are complementary: Prometheus is the engine, Grafana is the display.