Deployments

Deployments provide declarative updates for Pods and ReplicaSets. They’re the recommended way to manage stateless applications in Kubernetes.

Why Use Deployments?

Deployments offer several advantages over managing Pods directly:

Declarative updates - Define desired state
Rolling updates - Zero-downtime deployments
Rollback capability - Revert to previous versions
Scaling - Easily adjust replica count
Self-healing - Automatic Pod replacement

Creating a Deployment

Here’s a basic Deployment definition:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80

Create the Deployment:

kubectl apply -f deployment.yaml

Viewing Deployments

Check Deployment status:

# List Deployments
kubectl get deployments

# Detailed information
kubectl describe deployment nginx-deployment

# View ReplicaSets created by Deployment
kubectl get replicasets

# View Pods created by Deployment
kubectl get pods -l app=nginx

Scaling Deployments

Scale up or down easily:

# Scale using kubectl
kubectl scale deployment nginx-deployment --replicas=5

# Edit Deployment directly
kubectl edit deployment nginx-deployment

Update the YAML:

spec:
  replicas: 5

Rolling Updates

Update container image:

# Update image
kubectl set image deployment/nginx-deployment nginx=nginx:1.22

# Check rollout status
kubectl rollout status deployment/nginx-deployment

# View rollout history
kubectl rollout history deployment/nginx-deployment

Update Strategies

RollingUpdate (Default)

Gradually replaces old Pods with new ones:

spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1        # Max new Pods during update
      maxUnavailable: 0  # Max unavailable Pods

Recreate

Kills all Pods before creating new ones:

spec:
  strategy:
    type: Recreate

Rollback

Undo a deployment:

# Rollback to previous version
kubectl rollout undo deployment/nginx-deployment

# Rollback to specific revision
kubectl rollout undo deployment/nginx-deployment --to-revision=2

# Pause a rollout
kubectl rollout pause deployment/nginx-deployment

# Resume a rollout
kubectl rollout resume deployment/nginx-deployment

Advanced Configuration

Resource Limits

spec:
  template:
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        resources:
          requests:
            memory: "128Mi"
            cpu: "250m"
          limits:
            memory: "256Mi"
            cpu: "500m"

Environment Variables

env:
- name: ENVIRONMENT
  value: "production"
- name: DATABASE_URL
  valueFrom:
    secretKeyRef:
      name: db-secret
      key: url

Health Checks

livenessProbe:
  httpGet:
    path: /healthz
    port: 8080
  initialDelaySeconds: 30
  periodSeconds: 10

readinessProbe:
  httpGet:
    path: /ready
    port: 8080
  initialDelaySeconds: 5
  periodSeconds: 5

Labels and Selectors

Labels organize and select resources:

metadata:
  labels:
    app: nginx
    environment: production
    tier: frontend
spec:
  selector:
    matchLabels:
      app: nginx
    matchExpressions:
    - key: environment
      operator: In
      values:
      - production
      - staging

Deployment Status

Monitor Deployment health:

# Check if Deployment is ready
kubectl get deployment nginx-deployment

# Expected output
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   3/3     3            3           5m

# Detailed conditions
kubectl get deployment nginx-deployment -o yaml | grep -A 5 conditions

Best Practices

Set resource requests and limits - Ensure proper scheduling
Use health checks - Enable automatic recovery
Configure update strategy - Control rollout behavior
Use specific image tags - Avoid latest tag
Set Pod disruption budgets - Maintain availability
Use proper labels - Enable filtering and organization
Test rollouts - Use staging environments

Troubleshooting

Common issues:

# Pods not starting
kubectl describe deployment nginx-deployment
kubectl logs deployment/nginx-deployment

# Update stuck
kubectl rollout status deployment/nginx-deployment
kubectl get events --sort-by=.metadata.creationTimestamp

# Image pull errors
kubectl describe pod <pod-name>

Cleanup

Delete a Deployment:

# Delete Deployment (also deletes Pods)
kubectl delete deployment nginx-deployment

# Delete using YAML file
kubectl delete -f deployment.yaml

Next Steps

Now that you understand Deployments, let’s explore Services - how to expose your applications to network traffic.