# Create, View and Destroy a Replica Set

Paul Tomoiu

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Kubernetes

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Published 2022-12-03

This tutorial explains to you how to create, view and destroy a Replica Set in a Kubernetes cluster.

# Replica Set - explanation

When you deploy pods there is no mechanism to monitor that pod. If the pod fails it will not be created again.

A Replica Set is a layer of abstraction over pods. When a Replica Set is created a Controller monitors the pods to ensure that we have the desired number of pods running on Kubernetes cluster.

Info

One Replica Set is associated with only one pod type (created from the same image).

A Replica Set has a selector which identifies the pods it takes care of. If you have a Pod with label matching the ReplicaSet label, ReplicaSet will take control over the pod.

For instance, if you deploy Replica Set with 3 replicas and Pod with labels matching the Replica Set labels was deployed before that, then RS will spawn only 2 Pods with the matching labels.

ReplicaSet helps perform load balancing between multiple instances of the pod.

# Create a Replica Set in a Kubernetes cluster

Info

These examples are done on Minikube.

In order to create a Replica Set, we need to create a file as my-first-replica-set.yml which describes the Replica Set we want to create:

my-first-replica-set.yml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: nginx-rs
spec:
  replicas: 2
  selector:
    matchLabels:
      app: app1
  template:
    metadata:
      labels:
        app: app1
    spec:
      containers:
      - name: my-container
        image: nginx:1.14.2

The following command will create a new Replica Set:

kubectl apply -f my-first-replica-set.yml

Info

kubectl command POSTs the manifest to the API server.
Because we define what we want to have, this is considered a Declarative way of creating Replica Sets.
When we tell Kubernetes what exactly to do this is the Imperative approach. Instead apply we are using create or replace. Using the imperative approach, you’d need to use the kubectl scale command to change the replica count of an existing deployment.

# View Replica Set information

We can run the following command to see the result:

kubectl get rs

NAME       DESIRED   CURRENT   READY   AGE
nginx-rs   2         2         2       2m47s

Get more information on a specific Replica Set:

kubectl describe rs nginx-rs

In my case the result is:

Name:         nginx-rs
Namespace:    default
Selector:     app=app1
Labels:       <none>
Annotations:  <none>
Replicas:     2 current / 2 desired
Pods Status:  2 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  app=app1
  Containers:
   my-container:
    Image:        nginx:1.14.2
    Port:         <none>
    Host Port:    <none>
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age    From                   Message
  ----    ------            ----   ----                   -------
  Normal  SuccessfulCreate  3m14s  replicaset-controller  Created pod: nginx-rs-v2gd2
  Normal  SuccessfulCreate  3m14s  replicaset-controller  Created pod: nginx-rs-fsf48

# Destroy a Replica Set in a Kubernetes cluster

Delete the Replica Set created above:

kubectl delete rs nginx-rs