Deployments

Kubernetes Deployments automate application upgrades, scaling, and self-healing in production environments. They enable rolling updates, controlled rollbacks, and pause/resume capabilities—all without downtime. In this guide, you’ll learn how Deployments manage ReplicaSets and Pods, define a Deployment manifest, and inspect your resources using kubectl.

Why Use a Deployment?

• Rolling Updates: Replace pods one by one to avoid service interruption.
• Rollbacks: Instantly revert to a previous version if something goes wrong.
• Pause & Resume: Apply several changes as a batch and resume when ready.
• Declarative Scaling: Increase or decrease replicas in your manifest.

How Deployments Work

A Deployment sits above ReplicaSets and Pods:

1. Pod: The basic execution unit (one or more containers).
2. ReplicaSet: Ensures a specified number of pod replicas run at any time.
3. Deployment: Manages ReplicaSets and orchestrates updates, rollbacks, and scaling.

Resource Comparison

Writing a Deployment Manifest

Create a YAML file (deployment-definition.yml) to declare your desired state:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
    type: front-end
spec:
  replicas: 3
  selector:
    matchLabels:
      type: front-end
  template:
    metadata:
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
        - name: nginx-container
          image: nginx:latest
          ports:
            - containerPort: 80

• apiVersion: The API group (apps/v1).
• kind: Must be Deployment.
• metadata: Identifies the Deployment (name and labels).
• spec.replicas: Desired number of pods.
• spec.selector: Matches labels on pods.
• spec.template: Defines the pod spec, just like a ReplicaSet.

Deploying and Inspecting Resources

1. Create or update the Deployment

   kubectl apply -f deployment-definition.yml
   

2. View Deployments

   kubectl get deployments
   

   Example output:

   NAME              READY   UP-TO-DATE   AVAILABLE   AGE
   myapp-deployment  3/3     3            3           30s
   

3. List ReplicaSets

   kubectl get rs
   

4. Check Pods

   kubectl get pods
   

5. See All Resources

   kubectl get all
   

kubectl rollout undo deployment/myapp-deployment

Next Steps & References

• Learn more about Kubernetes Deployments
• Explore the kubectl Cheat Sheet
• Official Kubernetes Documentation