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Day 2 of 5
⏱ ~60 minutes
Kubernetes in 5 Days — Day 2

Deployments and ReplicaSets

Create Deployments for zero-downtime rollouts, scale replicas, roll back versions, and use ConfigMaps for configuration.

Deployments

A Deployment manages a ReplicaSet, which manages Pods. You tell the Deployment what you want (image, replicas) and Kubernetes makes it happen.

deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-app
  template:
    metadata:
      labels:
        app: web-app
    spec:
      containers:
      - name: web
        image: nginx:1.24
        ports:
        - containerPort: 80
        resources:
          requests:
            memory: '64Mi'
            cpu: '100m'
          limits:
            memory: '128Mi'
            cpu: '200m'
Managing Deployments
kubectl apply -f deployment.yaml
kubectl get deployments
kubectl get pods  # should show 3 pods

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

# Update image (triggers rolling update)
kubectl set image deployment/web-app web=nginx:1.25

# Watch the rollout
kubectl rollout status deployment/web-app

# Roll back
kubectl rollout undo deployment/web-app
kubectl rollout history deployment/web-app
ConfigMap
# configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  APP_ENV: production
  LOG_LEVEL: info

# Use in a Deployment
env:
- name: APP_ENV
  valueFrom:
    configMapKeyRef:
      name: app-config
      key: APP_ENV
📝 Day 2 Exercise
Roll Out and Roll Back
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Day 2 Summary

  • Deployments manage the desired state. Change the spec, Kubernetes figures out how to get there.
  • Rolling updates: Kubernetes replaces Pods one at a time. No downtime during updates.
  • kubectl rollout undo reverts to the previous version instantly.
  • ConfigMaps inject configuration as environment variables without rebuilding the image.
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Day 1: Pods and the Kubernetes Architecture
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Day 3: Services and Networking
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