K8s resource: Deployment

What is a Deployment?

A Deployment in Kubernetes is a workload resource used to manage the deployment, scaling, and updating of stateless application pods.

A Deployment is used to ensure that a specific number of pod replicas are running and available at all times. If a pod crashes or is deleted, the Deployment resource will create a new one to replace it.

It also performs rolling updates (rolls out new updates one pod at a time) to ensure your application is always available even during new deployments.

Example Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: web
        image: nginx:1.25
        ports:
        - containerPort: 80

This config will tell K8s to:

• Always ensure 3 pods of the nginx:1.25 container are running.
• Update the pods one by one when you change the image.

YAML lines:

• apiVersion
• kind: The kind of K8s component
• metadata
  • name: The name of the deployment
  • labels:
    • app: ?
• spec
  • replicas: How many replicas of the Pods.
  • selector
    • matchLabels
      • app: ?
  • template
    • metadata
      • labels
        • app