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Hello World Example

This is the simplest possible Celestra application - a basic web server that displays "Hello, World!". Perfect for getting started with Celestra.

🎯 What You'll Build

A simple web application that: - Runs a basic web server - Displays a "Hello, World!" message - Is accessible via HTTP - Can be scaled horizontally - Includes basic health checks

📋 Prerequisites

Before starting, ensure you have:

  • Celestra installed (pip install celestra)
  • A Kubernetes cluster (minikube, kind, or cloud)
  • kubectl configured
  • Basic understanding of Python

🚀 Step 1: Create the Application

Create a file called hello_world.py:

from celestra import App

# Create a simple web application
hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .replicas(2)
    .resources(cpu="100m", memory="128Mi")
    .health_check("/")
    .expose())

# Generate Kubernetes manifests
hello_app.generate().to_yaml("./hello-world/")

print("✅ Hello World manifests generated in ./hello-world/")

🎯 Step 2: Run the Application

# Run the application
python hello_world.py

# Deploy to Kubernetes
kubectl apply -f ./hello-world/

🔍 Step 3: Verify the Deployment

# Check if pods are running
kubectl get pods

# Check if service is created
kubectl get services

# Port forward to access the application
kubectl port-forward svc/hello-world 8080:80

Now open your browser and go to http://localhost:8080 to see "Hello, World!"

📊 What Was Created

Celestra generated the following Kubernetes resources:

1. Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world
spec:
  replicas: 2
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
      - name: hello-world
        image: nginxdemos/hello:latest
        ports:
        - containerPort: 80
        resources:
          requests:
            cpu: 100m
            memory: 128Mi
        livenessProbe:
          httpGet:
            path: /
            port: 80

2. Service

apiVersion: v1
kind: Service
metadata:
  name: hello-world
spec:
  selector:
    app: hello-world
  ports:
  - port: 80
    targetPort: 80
  type: ClusterIP

🔧 Customization Options

Add Environment Variables

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .replicas(2)
    .env("MESSAGE", "Hello from Celestra!")
    .env("ENVIRONMENT", "development")
    .expose())

Add Configuration

from celestra import ConfigMap

# Configuration
config = ConfigMap("hello-config").add("message", "Hello from ConfigMap!")

# Add to application
hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .add_config(config)
    .expose())

Add Health Checks

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .health_check("/")
    .liveness_probe("/")
    .readiness_probe("/")
    .expose())

Scale the Application

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .replicas(5)  # Scale to 5 replicas
    .expose())

🎯 Advanced Features

Add Resource Limits

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .resources(
        cpu="100m",           # CPU request
        memory="128Mi",        # Memory request
        cpu_limit="200m",      # CPU limit
        memory_limit="256Mi"   # Memory limit
    )
    .expose())

Add Rolling Update Strategy

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .rolling_update(
        max_surge=1,
        max_unavailable=0
    )
    .expose())

Add Annotations and Labels

hello_app = (App("hello-world")
    .image("nginxdemos/hello:latest")
    .port(80)
    .add_label("environment", "development")
    .add_label("team", "platform")
    .add_annotation("description", "Simple hello world application")
    .expose())

🔍 Testing the Application

Health Check

# Check if the application is healthy
kubectl get pods -l app=hello-world

# Check logs
kubectl logs -l app=hello-world

Load Testing

# Install hey for load testing
go install github.com/rakyll/hey@latest

# Test the application
hey -n 1000 -c 10 http://localhost:8080

Scale Testing

# Scale the application
kubectl scale deployment hello-world --replicas=5

# Check the scaling
kubectl get pods -l app=hello-world

🚀 Generate Different Outputs

Celestra supports multiple output formats:

# Kubernetes YAML
hello_app.generate().to_yaml("./k8s/")

# Docker Compose (for local development)
hello_app.generate().to_docker_compose("./docker-compose.yml")

# Helm Chart
hello_app.generate().to_helm_chart("./charts/")

# Kustomize
hello_app.generate().to_kustomize("./kustomize/")

🔧 Troubleshooting

Common Issues

1. Pod Not Starting 

# Check pod status
kubectl describe pod -l app=hello-world

# Check events
kubectl get events --sort-by=.metadata.creationTimestamp

2. Service Not Accessible 

# Check service
kubectl get service hello-world

# Check endpoints
kubectl get endpoints hello-world

3. Image Pull Issues 

# Check image pull status
kubectl describe pod -l app=hello-world | grep -A 10 Events

Debug Commands

# Get detailed pod information
kubectl describe pod -l app=hello-world

# Check pod logs
kubectl logs -l app=hello-world

# Execute into pod
kubectl exec -it $(kubectl get pod -l app=hello-world -o jsonpath='{.items[0].metadata.name}') -- /bin/sh

# Check service connectivity
kubectl run test --image=busybox --rm -it --restart=Never -- wget -O- http://hello-world

🚀 Next Steps

Ready to build more complex applications? Try these examples:

  1. NGINX Web Server - Deploy a web server
  2. Node.js Application - Deploy a Node.js app
  3. [Database Deployment] - Coming soon - Database examples will be added here
  4. [Production Platform] - Coming soon - Production platform examples will be added here

Ready to build something more complex? Check out the NGINX Web Server example or jump to Production Deployments!