🧱 Pods, ReplicaSets & Deployments – Managing Kubernetes Workloads

In our previous posts, we explored Kubernetes Components and how Kubernetes Architecture functions behind the scenes.

Now it’s time to dive into how applications actually run on Kubernetes — starting with:

  • Pods
  • ReplicaSets
  • Deployments

What is a Pod?

A Pod is the smallest unit of deployment in Kubernetes. It represents:

  • One or more containers that share storage/network
  • Run as a single logical unit

Multi-container Pods

Sometimes a Pod has sidecar containers — for example:

  • One container runs your app
  • Another handles logging, proxying, or configuration

Pod Lifecycle

  • Pods are ephemeral: if a Pod dies, Kubernetes creates a new one
  • For that reason, Pods are almost always managed by higher-level objects like ReplicaSets

What is a ReplicaSet?

A ReplicaSet ensures that a specified number of identical Pods are running at any given time.

  • It watches the state of your cluster and automatically replaces failed Pods
  • Each ReplicaSet is tied to a specific template (i.e., Pod spec)

However, you typically won’t create ReplicaSets manually — they’re usually managed by Deployments.

What is a Deployment?

A Deployment provides declarative updates for Pods and ReplicaSets.
Think of it as a blueprint that defines:

  • How many replicas (Pods) you want
  • Which image to deploy
  • How to perform updates or rollbacks

Example YAML Snippet

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: my-app
        image: my-app-image:v1

✅ This will ensure 3 Pods are always running using the my-app-image:v1 image.

Updates & Rollbacks

You can update the image version:

kubectl set image deployment/my-app my-app=my-app-image:v2

Roll back to the previous version:

kubectl rollout undo deployment/my-app

Conclusion

Pods are the basic execution unit

ReplicaSets ensure Pods are always available

Deployments manage ReplicaSets declaratively and allow updates & rollback

These three resources form the core of how apps run in Kubernetes.

Next, we’ll look at how to expose those apps using Services — including ClusterIP, NodePort, and LoadBalancer types. ☸️