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Kubernetes Exercise: Deploy Loki Stack with Log Collector and Sample App

Objectives

By the end of this exercise, you will:

  1. Deploy the Loki Stack (Loki, Promtail, and Grafana) using Helm.
  2. Deploy a sample application that emits logs.
  3. View the application logs in Grafana using LogQL.

Prerequisites

  • A Kubernetes cluster (minikube, kind, cloud, etc.)
  • kubectl installed and configured
  • helm installed (https://helm.sh/docs/intro/install/)
  • Optional: port 3000 open on localhost for Grafana

Step 1: Add and Install Loki Stack with Helm

helm repo add grafana https://grafana.github.io/helm-charts
helm repo update

# Create a monitoring namespace
kubectl create namespace monitoring

# Install the Loki stack (Loki + Promtail + Grafana)
helm install loki-stack grafana/loki-stack --namespace monitoring \
  --set grafana.enabled=true \
  --set promtail.enabled=true \
  --set loki.persistence.enabled=false \
  --set grafana.service.type=NodePort

Wait until everything is ready:

kubectl get pods -n monitoring

Step 2: Access Grafana UI

Port forward Grafana:

kubectl port-forward -n monitoring service/loki-stack-grafana 3000:80

Then open: http://localhost:3000

Login credentials:

  • User: admin
  • Password: prom-operator (default for Loki Helm chart)

Step 3: Deploy a Sample App with Logs

Here’s a simple "log generator" app that prints messages to stdout.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: log-emitter
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: log-emitter
  template:
    metadata:
      labels:
        app: log-emitter
    spec:
      containers:
      - name: logger
        image: busybox
        command: ["/bin/sh"]
        args: ["-c", "while true; do echo Hello from $(hostname); sleep 5; done"]

Apply it:

kubectl apply -f log-emitter.yaml

Step 4: View Logs in Grafana

Add the Loki data source (if not already added)

  1. Go to Grafana UI → ⚙️ Configuration → Data Sources
  2. Click Add data source → choose Loki
  3. URL: http://loki-stack:3100
  4. Click Save & Test

Explore logs

  1. Go to Explore
  2. Select Loki as the datasource
  3. Use a query like:
{app="log-emitter"}

You should see logs like:

Hello from log-emitter-xxxx

Bonus Tasks

  • Scale the deployment to replicas: 3 and observe the logs.
  • Modify the log message (e.g., include timestamps or random IDs).
  • Add a label to logs and filter by it in LogQL.

Cleanup

kubectl delete deployment log-emitter
helm uninstall loki-stack -n monitoring
kubectl delete namespace monitoring