Deployments and ReplicaSets

A Deployment is the controller you will use most often. It creates and manages ReplicaSets to keep replica counts and version updates under control.

Key points

• ReplicaSet owns replica counts
• Deployment owns version updates
• Rollbacks are managed by the Deployment

Example Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: api
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  selector:
    matchLabels:
      app: api
  template:
    metadata:
      labels:
        app: api
    spec:
      containers:
        - name: api
          image: nginx:1.25

Rollout and rollback

kubectl rollout status deploy/api
kubectl rollout history deploy/api
kubectl rollout undo deploy/api

Practical notes

• Start with a quick inventory: kubectl get nodes, kubectl get pods -A, and kubectl get events -A.
• Compare desired vs. observed state; kubectl describe usually explains drift or failed controllers.
• Keep names, labels, and selectors consistent so Services and controllers can find Pods.

Quick checklist

• The resource matches the intent you described in YAML.
• Namespaces, RBAC, and images are correct for the target environment.
• Health checks and logs are in place before promotion.

References

• Deployments
• ReplicaSets