Deploy Highly Available Applications Using Kubernetes ReplicationController (nginx:latest)

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Ques:-  

DevOps team is establishing a ReplicationController to deploy multiple pods for hosting applications that require a highly available infrastructure. Follow the specifications below to create the ReplicationController:

Create a ReplicationController using the nginx image with latest tag, and name it nginx-replicationcontroller.

Assign labels app as nginx_app, and type as front-end. Ensure the container is named nginx-container and set the replica count to 3.

All pods should be running state post-deployment.


Ans:-

🔍 What is a ReplicationController?

A ReplicationController (RC) is a Kubernetes object that:

• Ensures a fixed number of pod replicas are running.
• Automatically creates new pods if some fail or are deleted.
• Uses a label selector to manage the pods it controls.

⚠️ Note: ReplicationController has largely been replaced by Deployments and ReplicaSets, which offer more advanced features like rolling updates and rollbacks.

---

✅ Use Cases of ReplicationController

• High Availability: Ensures multiple instances of an application are always running.
• Fault Tolerance: Automatically replaces failed pods.
• Load Distribution: Helps distribute traffic across multiple pod replicas.
• Legacy Support: Still used in older Kubernetes setups or for backward compatibility.

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🆚 ReplicationController vs ReplicaSet

Feature	ReplicationController	ReplicaSet
Label selector	Exact match only	Supports set-based
Rolling updates	Not supported	Supported via Deployment
Preferred usage	Legacy	Modern Kubernetes

raj@jumphost ~$ cat pod.yaml 

apiVersion: v1

kind: ReplicationController

metadata:

  name: nginx-replicationcontroller

  labels:

    app: nginx_app

    type: front-end

spec:

  replicas: 3

  selector:

    app: nginx_app

    type: front-end

  template:

    metadata:

      labels:

        app: nginx_app

        type: front-end

    spec:

      containers:

      - name: nginx-container

        image: nginx:latest

        ports:

        - containerPort: 80

raj@jumphost ~$ kubectl apply -f pod.yaml 

replicationcontroller/nginx-replicationcontroller created

raj@jumphost ~$ kubectl get replicationcontroller

NAME                          DESIRED   CURRENT   READY   AGE

nginx-replicationcontroller   3         3         3       59s

raj@jumphost ~$ kubectl get pod

NAME                                READY   STATUS    RESTARTS   AGE

nginx-replicationcontroller-7mf6t   1/1     Running   0          68s

nginx-replicationcontroller-kbmqx   1/1     Running   0          68s

nginx-replicationcontroller-n82rj   1/1     Running   0          68s

raj@jumphost ~$