Kubernetes for Application Development: A Practical Guide

Kubernetes has become the default infrastructure layer for complex distributed applications, but it carries significant operational complexity. This guide focuses on what developers need to know to deploy and operate applications effectively on Kubernetes — without spending weeks on certificate management and etcd backups.

Core Concepts Every Developer Needs

# Complete application deployment in Kubernetes
# 1. Deployment — manages ReplicaSets, handles rolling updates
apiVersion: apps/v1
kind: Deployment
metadata:
  name: api-server
  namespace: production
  labels:
    app: api-server
    version: "1.2.3"
spec:
  replicas: 3
  selector:
    matchLabels:
      app: api-server
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1         # Allow 1 extra pod during update
      maxUnavailable: 0   # Never reduce below desired count
  template:
    metadata:
      labels:
        app: api-server
    spec:
      containers:
        - name: api
          image: registry.example.com/api-server:1.2.3
          ports:
            - containerPort: 8080
          env:
            - name: NODE_ENV
              value: production
            - name: DATABASE_URL
              valueFrom:
                secretKeyRef:
                  name: api-secrets
                  key: database-url
          resources:
            requests:
              memory: "256Mi"
              cpu: "100m"
            limits:
              memory: "512Mi"
              cpu: "500m"
          readinessProbe:
            httpGet:
              path: /health/ready
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 5
          livenessProbe:
            httpGet:
              path: /health/live
              port: 8080
            initialDelaySeconds: 30
            periodSeconds: 10
---
# 2. Service — stable DNS name and load balancing
apiVersion: v1
kind: Service
metadata:
  name: api-server
  namespace: production
spec:
  selector:
    app: api-server
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
  type: ClusterIP
---
# 3. HorizontalPodAutoscaler — scale based on load
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: api-server-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: api-server
  minReplicas: 3
  maxReplicas: 20
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 70

Helm for Package Management

# Install app with Helm
helm install my-app ./charts/api-server   --namespace production   --set image.tag=1.2.3   --set replicas=3   --values production-values.yaml

# Upgrade with zero downtime
helm upgrade my-app ./charts/api-server   --namespace production   --set image.tag=1.3.0   --atomic  # Rollback automatically if upgrade fails
  --timeout 5m

# Rollback if needed
helm rollback my-app 1  # Roll back to revision 1

Health Checks (Non-Negotiable)

Every application deployed to Kubernetes must implement proper health endpoints:

// Express.js health endpoints
app.get('/health/live', (req, res) => {
  // Liveness: is the process running? Always return 200 if the server is up.
  // Kubernetes restarts the pod if this fails.
  res.json({ status: 'alive', timestamp: new Date().toISOString() })
})

app.get('/health/ready', async (req, res) => {
  // Readiness: is the app ready to serve traffic?
  // Kubernetes removes pod from load balancer if this fails.
  try {
    await db.query('SELECT 1')  // Check database connectivity
    res.json({ status: 'ready', database: 'connected' })
  } catch {
    res.status(503).json({ status: 'not ready', database: 'disconnected' })
  }
})

When NOT to Use Kubernetes

Kubernetes adds significant operational overhead. Consider alternatives:

Use Kubernetes when: you have 10+ services, need sophisticated deployment patterns, require fine-grained resource control, or are building an internal platform for multiple teams.

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See also: DevOps Consulting Company Guide · Cloud Migration Services Guide