Prometheus for metrics collection in Kubernetes - Commands & Configuration

Introduction

Prometheus helps you collect and store data about how your applications and servers are performing. It solves the problem of knowing what is happening inside your system by gathering metrics you can watch and analyze.

When you want to monitor the health of your Kubernetes applications in real time.

When you need to track how much CPU or memory your services are using.

When you want to set alerts to notify you if something goes wrong in your system.

When you want to visualize performance trends over time with graphs.

When you need a reliable way to collect metrics from multiple servers and containers.

Config File - prometheus-deployment.yaml

prometheus-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: prometheus
  labels:
    app: prometheus
spec:
  replicas: 1
  selector:
    matchLabels:
      app: prometheus
  template:
    metadata:
      labels:
        app: prometheus
    spec:
      containers:
      - name: prometheus
        image: prom/prometheus:v2.44.0
        args:
        - --config.file=/etc/prometheus/prometheus.yml
        ports:
        - containerPort: 9090
        volumeMounts:
        - name: config-volume
          mountPath: /etc/prometheus/
      volumes:
      - name: config-volume
        configMap:
          name: prometheus-config
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: prometheus-config
data:
  prometheus.yml: |
    global:
      scrape_interval: 15s
    scrape_configs:
      - job_name: 'kubernetes'
        static_configs:
          - targets: ['localhost:9090']

This file creates a Prometheus deployment in Kubernetes with one replica.

The ConfigMap holds the Prometheus configuration, telling it to scrape metrics every 15 seconds from itself (localhost:9090).

The deployment mounts this config so Prometheus knows where to get its settings.

Commands

This command creates the Prometheus deployment and its configuration in your Kubernetes cluster.

Terminal

kubectl apply -f prometheus-deployment.yaml

Expected Output

deployment.apps/prometheus created

configmap/prometheus-config created

This command checks if the Prometheus pod is running by listing pods with the label 'app=prometheus'.

Terminal

kubectl get pods -l app=prometheus

Expected Output

NAME                        READY   STATUS    RESTARTS   AGE

prometheus-6d4b7f7f7f-abcde 1/1     Running   0          30s

→

-l - Filter pods by label

This command forwards your local machine's port 9090 to the Prometheus pod's port 9090 so you can access the Prometheus web interface in your browser at http://localhost:9090.

Terminal

kubectl port-forward deployment/prometheus 9090:9090

Expected Output

Forwarding from 127.0.0.1:9090 -> 9090

Forwarding from [::1]:9090 -> 9090

Key Concept

If you remember nothing else from this pattern, remember: Prometheus collects metrics by regularly scraping configured targets and stores them for monitoring and alerting.

Common Mistakes

Not creating the ConfigMap before deploying Prometheus.

Prometheus needs its configuration file to know what to monitor; without it, it won't start properly.

Always apply the ConfigMap with the Prometheus configuration before or together with the deployment.

Trying to access Prometheus without port-forwarding or a service.

Prometheus runs inside the cluster and is not accessible from outside by default.

Use kubectl port-forward or create a Kubernetes service to expose Prometheus.

Setting scrape targets incorrectly in prometheus.yml.

If targets are wrong or unreachable, Prometheus will not collect any metrics.

Verify targets are correct and reachable from the Prometheus pod.

Summary

Create a ConfigMap with Prometheus settings to tell it what to monitor.

Deploy Prometheus in Kubernetes using a Deployment that mounts the ConfigMap.

Use kubectl commands to apply the configuration, check pod status, and access the Prometheus UI.