Kubernetes Basics

Kubernetes (K8s) orchestrates containerized applications at scale. Let's understand the fundamentals.

Core Concepts

Pods

The smallest deployable unit:

# pod.yaml
apiVersion: v1
kind: Pod
metadata:
 name: my-app
spec:
 containers:
 - name: app
 image: myapp:1.0
 ports:
 - containerPort: 3000

Deployments

Manage pod replicas and updates:

# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
 name: my-app
spec:
 replicas: 3
 selector:
 matchLabels:
 app: my-app
 template:
 metadata:
 labels:
 app: my-app
 spec:
 containers:
 - name: app
 image: myapp:1.0
 ports:
 - containerPort: 3000
 resources:
 limits:
 memory: "128Mi"
 cpu: "500m"

Services

Expose pods to network:

# service.yaml
apiVersion: v1
kind: Service
metadata:
 name: my-app-service
spec:
 selector:
 app: my-app
 ports:
 - port: 80
 targetPort: 3000
 type: LoadBalancer

Essential Commands

# Apply configuration
kubectl apply -f deployment.yaml

# Get resources
kubectl get pods
kubectl get deployments
kubectl get services

# Describe a resource
kubectl describe pod my-app

# View logs
kubectl logs my-app-pod

# Execute command in pod
kubectl exec -it my-app-pod -- /bin/sh

# Scale deployment
kubectl scale deployment my-app --replicas=5

ConfigMaps and Secrets

Manage configuration:

# configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
 name: app-config
data:
 DATABASE_HOST: "db.example.com"
 LOG_LEVEL: "info"

---
# secret.yaml
apiVersion: v1
kind: Secret
metadata:
 name: app-secrets
type: Opaque
data:
 API_KEY: YXBpLWtleS12YWx1ZQ== # base64 encoded

Use in deployment:

spec:
 containers:
 - name: app
 envFrom:
 - configMapRef:
 name: app-config
 - secretRef:
 name: app-secrets

Ingress

Route external traffic:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
 name: my-ingress
spec:
 rules:
 - host: myapp.example.com
 http:
 paths:
 - path: /
 pathType: Prefix
 backend:
 service:
 name: my-app-service
 port:
 number: 80

Conclusion

Kubernetes is essential for modern deployments. Start small, learn the basics, then explore advanced features.