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Concept

Kubernetes: Deployments

How Deployments manage rolling updates and rollbacks over ReplicaSets, with an example manifest.

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A Deployment provides declarative updates for Pods and ReplicaSets, enabling application scaling, rolling updates, and rollbacks. It maintains the desired state of applications and ensures that the right number of Pods are always running.

Deployments use a default RollingUpdate strategy for seamless version transitions but can also use the Recreate strategy for disruptive updates. When a Deployment is updated (e.g., changing the image version), it creates a new ReplicaSet while gradually replacing Pods from the old ReplicaSet.

Example YAML manifest:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-deployment
  template:
    metadata:
      labels:
        app: nginx-deployment
    spec:
      containers:
        - name: nginx
          image: nginx:1.20.2
          ports:
            - containerPort: 80

Key commands:

Terminal window
kubectl create -f def-deploy.yaml
kubectl create deployment nginx-deployment \
--image=nginx:1.20.2 --port=80 --replicas=3


kubectl create deployment nginx-deployment \
--image=nginx:1.20.2 --port=80 --replicas=3 \
--dry-run=client -o yaml > nginx-deploy.yaml


kubectl create -f nginx-deploy.yaml
kubectl create -f nginx-deploy.json

Deployment updates result in new ReplicaSets being created (e.g., updating from image 1.20.2 to 1.21.5), transitioning Pods from one revision to the next through a rolling update process.