Day 08/40 Days of K8s: Understanding Deployment, RPS, and Replication Controllers

While pods run containers, the real power of Kubernetes lies in features like self-healing and High availability.These are achieved using Deployments.

1. Pod: Abstraction of containers

2. Deployment: Abstraction of pods

In real-world scenarios, we typically create Deployments rather than individual pods.

Challenges with pod?🤔

1. High Load: How does a pod handle numerous requests?

2. Pod Crashes: What happens when a pod fails (given the ephemeral nature of containers)?

Solution: SELF-HEALING, HIGH AVAILABILITY🛠️🚀

Replication Controller and ReplicaSet

Replication Controller and ReplicaSet are used to maintain pod availability at any given time. The Replication Controller, a legacy object implements control loop mechanism, ensures a specified number of pod replicas are always running, creating new identical pods before existing ones terminate.

ReplicaSet, a latest version not only manages pods across nodes but can also create new nodes if existing ones lack resources. Both compare the desired and actual state of the cluster, with ReplicaSet offering enhanced pod selection capabilities.

ReplicaSet vs Replication Controller

• Replication Controller: Only manages pods created as part of that replication controller

• ReplicaSet: Can manage existing pods not originally part of the ReplicaSet using selectors and match labels.

Deployment

Additional functionality to ReplicaSet, all the version upgrades rollout to pods at the same time which intern causes downtime. Deployment does the rollout a version in a rolling update fashion. In case of issues with the new version rollout we can still rollback to previous version with deployment.

Remember: Deployments manage ReplicaSets, which in turn manage pods.

Let's get into Hands on......

1️⃣ TASK: 1

✅ Create a new Replicaset based on the nginx image with 3 replicas

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-replicaset
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80

• ✅ Update the replicas to 4 from the YAML

• ✅ Update the replicas to 6 from the command line

2️⃣ TASK 2

• ✅ Create a Deployment named nginx with 3 replicas. The Pods should use the nginx:1.23.0 image and the name nginx. The Deployment uses the label tier=backend. The Pod template should use the label app=v1

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  labels:
    tier: backend
spec:
  replicas: 3
  selector:
    matchLabels:
      app: v1
  template:
    metadata:
      labels:
        app: v1
    spec:
      containers:
      - name: nginx
        image: nginx:1.23.0
        ports:
        - containerPort: 80

• ✅ List the Deployment and ensure the correct number of replicas is running.

• ✅ Update the image to nginx:1.23.4

• ✅ Verify that the change has been rolled out to all replicas.

• ✅ Assign the change cause "Pick up patch version" to the revision

kubectl annotate deployment/nginx kubernetes.io/change-cause="Pick up patch version"
deployment.apps/nginx annotated

• ✅ Scale the Deployment to 5 replicas, Have a look at the Deployment rollout history.

kubectl scale deploy/nginx --replicas=5
deployment.apps/nginx scaled

kubectl rollout history deploy/nginx
deployment.apps/nginx
REVISION  CHANGE-CAUSE
1         <none>
2         Pick up patch version

• ✅ Revert the Deployment to revision 1.

kubectl rollout undo deploy/nginx
deployment.apps/nginx rolled back

• ✅ Ensure that the Pods use the image nginx:1.23.0

  

#Kubernetes #ReplicaSet #ReplicationController #Deployment #Yaml #40DaysofKubernetes #CKASeries