🚀 Kubernetes Deployments

A Deployment is the most commonly used controller in Kubernetes. It manages ReplicaSets, allowing for:

• Declarative updates
• Rollbacks
• Scaling
• Easy rollout of changes

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✅ Why Use a Deployment?

Unlike a raw ReplicaSet, a Deployment offers high-level operations:

• Rollout new versions with zero downtime
• Automatically create new ReplicaSets
• Roll back to previous versions

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📦 Create a Deployment

Imperative Command

kubectl create deployment nginx --image=nginx

With Replicas

kubectl create deployment nginx --image=nginx --replicas=4

If --replicas is not accepted, scale it after:

kubectl scale deployment nginx --replicas=4

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✍️ Generate YAML Without Creating (Dry Run)

kubectl create deployment nginx --image=nginx --dry-run=client -o yaml > nginx-deployment.yaml

You can then customize and apply it:

kubectl apply -f nginx-deployment.yaml

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🧾 Sample Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.19
        ports:
        - containerPort: 80

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🔍 Inspect & Manage Deployments

kubectl get deployments
kubectl describe deployment <name>
kubectl edit deployment <name>
kubectl delete deployment <name>

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🔁 Rollouts & Rollbacks

View rollout status

kubectl rollout status deployment <name>

Roll back to previous version

kubectl rollout undo deployment <name>

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❌ Common Deployment Issues

Pods stuck in ImagePullBackOff

kubectl describe pod <pod-name>
# Check the Events section

Example Error

spec:
  containers:
  - name: app
    image: nonexistent-image  # leads to ImagePullBackOff

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🧠 Key Differences from ReplicaSet

Feature	Deployment	ReplicaSet
Manages RS?	✅ Yes	❌ No
Rollbacks	✅ Yes	❌ No
Rolling updates	✅ Yes	❌ Manual only
Recommended?	✅ Production default	🚫 Not preferred

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✅ Summary

• Deployment is your go-to controller for managing stateless apps
• Use kubectl apply with YAML for full control
• Supports rollback, rollout, and declarative scaling
• Use kubectl rollout status to monitor updates
• Use Deployments unless you have a stateful or special-case workload