Managing Amazon EBS Volumes and Snapshots Across Regions

 📘 Kubernetes Notes – Labels, ReplicaSet & Deployment

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🔹 LABELS

Labels are key-value pairs attached to Kubernetes objects like:

• Pods

• ReplicaSets

• Deployments

• Services

• Nodes

They are mainly used for:

• Identification

• Grouping

• Selection

• Management

Features

• Can be added during creation or runtime

• Multiple labels per object allowed

• ReplicaSet/Service manages Pods only using labels

Example

kubectl run pod-1 --image=nginx --labels="env=dev,app=swiggy"
kubectl get pods --show-labels

Extra useful commands

kubectl label pod pod-1 tier=frontend
kubectl label pod pod-1 tier-
kubectl get pods -l env=dev

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🔹 SELECTORS

Selectors filter Pods using labels.

Used by:

• ReplicaSet

• Deployment

• Service

Types

1️⃣ Equality-based

app=paytm
env!=prod

2️⃣ Set-based

env in (dev,test)
env notin (prod)

Example

kubectl get pods -l app=paytm

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🔹 REPLICASET (RS)

ReplicaSet ensures desired number of Pods are always running.

Features

• Creates multiple replicas

• Auto recreates if Pod crashes/deletes

• All Pods use same template

• Uses Labels + Selectors

• Supports scaling

• No rolling updates (manual only)

Flow

ReplicaSet → Pods

Important

• ReplicationController = Old version

• ReplicaSet = New version

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ReplicaSet YAML

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: movies
  labels:
    app: paytm
spec:
  replicas: 3
  selector:
    matchLabels:
      app: paytm
  template:
    metadata:
      labels:
        app: paytm
    spec:
      containers:
      - name: cont1
        image: rahashaik/movies:latest

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ReplicaSet Commands

kubectl create -f rs.yml
kubectl get rs
kubectl get pods -o wide
kubectl describe rs movies
kubectl edit rs movies
kubectl delete rs movies
kubectl scale rs/movies --replicas=10
kubectl get pods -l app=paytm

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❌ ReplicaSet Limitations

• No rolling updates

• No rollback

• No version control

• Not preferred in production

👉 Mostly managed indirectly via Deployment.

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🔹 DEPLOYMENT

Deployment = ReplicaSet + Advanced Features

It is the recommended way to manage Pods in production.

Features

✅ Rolling updates
✅ Rollback
✅ Zero downtime
✅ Version history
✅ Easy scaling
✅ Self-healing

Flow

Deployment → ReplicaSet → Pods

---

Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: movies
  labels:
    app: paytm
spec:
  replicas: 3
  selector:
    matchLabels:
      app: paytm
  template:
    metadata:
      labels:
        app: paytm
    spec:
      containers:
      - name: cont1
        image: rahamshaik/mynetflix:1.0

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Deployment Commands

Create

kubectl create -f deployment.yml

List

kubectl get deploy
kubectl get rs
kubectl get pods

Scale

kubectl scale deploy movies --replicas=10

Edit image (update)

kubectl set image deploy/movies cont1=mynetflix:2.0

Rollout commands

kubectl rollout history deployment movies
kubectl rollout status deployment movies
kubectl rollout undo deployment movies
kubectl rollout pause deployment movies
kubectl rollout resume deployment movies
kubectl rollout undo deploy movies --to-revision=1

Delete

kubectl delete deploy movies

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🔹 Rolling Update Strategy (Important for Interviews)

Types

1️⃣ RollingUpdate (Default)

• No downtime

• Gradually replaces Pods

strategy:
  type: RollingUpdate
  rollingUpdate:
    maxUnavailable: 1
    maxSurge: 1

2️⃣ Recreate

• Deletes all Pods first

• Then creates new Pods

• Causes downtime

strategy:
  type: Recreate

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🔹 Useful Extra Concepts

Scale automatically (HPA)

kubectl autoscale deploy movies --cpu-percent=50 --min=2 --max=10

Check events

kubectl get events

Logs

kubectl logs pod-name
kubectl logs -f pod-name

Exec into container

kubectl exec -it pod-name -- /bin/bash

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🔹 Quick Comparison Table

Feature	ReplicaSet	Deployment
Scaling	✅	✅
Self-healing	✅	✅
Rolling update	❌	✅
Rollback	❌	✅
Version history	❌	✅
Production use	❌	✅