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Chapter 3.6 - Deployments

Learning Objectives​

By the end of this chapter, you will be able to:

  • Understand the role of Deployments
  • Create and manage Deployments
  • Perform rolling updates
  • Manage rollbacks
  • Scale Deployments

What is a Deployment?​

A Deployment manages ReplicaSets and provides declarative update, rollback, and scaling capabilities.

Advantages:

  • Version management
  • Rolling updates
  • Automatic rollbacks
  • Easy scaling

YAML Declaration​

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-deployment
  labels:
    app: web
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: nginx
        image: nginx:1.20
        ports:
        - containerPort: 80
        resources:
          requests:
            cpu: "100m"
            memory: "128Mi"
          limits:
            cpu: "500m"
            memory: "512Mi"
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0

Rolling Updates​

Process​

Strategies​

RollingUpdate (default):

  • Progressively replaces Pods
  • No service interruption
  • Configurable (maxSurge, maxUnavailable)

Recreate:

  • Deletes all old Pods
  • Creates new Pods
  • Service interruption

Updating a Deployment​

Method 1: Update the Image​

# Update the image
kubectl set image deployment/web-deployment nginx=nginx:1.21

# View the update status
kubectl rollout status deployment/web-deployment

Method 2: Edit the YAML​

# Edit the Deployment
kubectl edit deployment web-deployment

# Or modify the file and apply
kubectl apply -f deployment.yaml

Method 3: Patch​

# Modify a specific part
kubectl patch deployment web-deployment -p '{"spec":{"replicas":5}}'

Rollback​

View History​

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

# Details of a revision
kubectl rollout history deployment/web-deployment --revision=2

Perform a Rollback​

# Rollback to the previous version
kubectl rollout undo deployment/web-deployment

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

Scaling​

Manual Scaling​

# Increase the number of replicas
kubectl scale deployment web-deployment --replicas=5

# Or edit
kubectl edit deployment web-deployment

Automatic Scaling (HPA)​

# Create a Horizontal Pod Autoscaler
kubectl autoscale deployment web-deployment --min=2 --max=10 --cpu-percent=80

Useful Commands​

# View Deployments
kubectl get deployments

# Details of a Deployment
kubectl describe deployment web-deployment

# View created ReplicaSets
kubectl get replicasets

# Pause/Resume a rollout
kubectl rollout pause deployment/web-deployment
kubectl rollout resume deployment/web-deployment

Summary​

In this chapter, you learned:

Deployment: Manages ReplicaSets with advanced features
Rolling Updates: Updates without interruption
Rollback: Return to a previous version
Scaling: Manual or automatic (HPA)
Management: kubectl set image, rollout, scale

Next Steps​

Now that you have mastered Deployments:

Chapter 3.7: Deployment Strategies
Chapter 3.8: Health Checks

Troubleshooting​

Common Problems with Deployments​

Problem 1: Deployment does not create Pods​

Symptoms:

kubectl get deployment
# NAME    READY   UP-TO-DATE   AVAILABLE
# my-app  0/3     0            0

Solutions:

  1. Check the events:

    kubectl describe deployment my-app
    kubectl get events --sort-by='.lastTimestamp'

  2. Check the ReplicaSets:

    kubectl get replicasets
    kubectl describe replicaset <rs-name>

  3. Check resource quotas:

    kubectl describe quota

Problem 2: Rolling Update stalls​

Symptoms:

  • The deployment remains in "Updating" state
  • New pods do not start

Solutions:

  1. Check the events:

    kubectl describe deployment my-app

  2. Check available resources:

    kubectl top nodes
    kubectl describe nodes

  3. Check health checks:

    • Probes (liveness/readiness) can prevent the deployment
    • Check the pod logs

  4. Force rollback if necessary:

    kubectl rollout undo deployment/my-app

Problem 3: Pods in CrashLoopBackOff​

Symptoms:

kubectl get pods
# NAME                     READY   STATUS             RESTARTS
# my-app-xxx-123           0/1     CrashLoopBackOff   5

Solutions:

  1. Check the logs:

    kubectl logs <pod-name>
    kubectl logs <pod-name> --previous

  2. Check the configuration:

    kubectl describe pod <pod-name>

  3. Check resources:

    • CPU/Memory limits too low
    • Missing volumes
    • Incorrect Secrets/ConfigMaps

Problem 4: Scaling does not work​

Symptoms:

kubectl scale deployment my-app --replicas=5
# But still 3 pods

Solutions:

  1. Check quotas:

    kubectl describe quota

  2. Check node resources:

    kubectl describe nodes

  3. Check constraints:

    kubectl get deployment my-app -o yaml
    # Check nodeSelectors, affinity, etc.

Previous chapter: Chapter 3.5 - ReplicaSets
Next chapter: Chapter 3.7 - Deployment Strategies
Back to module: Module 3 - Pods and Deployments

Chapter created: December 2024