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Create ReplicaSets

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Applies to: AKS on Azure Stack HCI 22H2, AKS on Windows Server

This article describes how to create, scale, and delete ReplicaSets in AKS enabled by Azure Arc. ReplicaSets are used to ensure that a stable set of replica pods are running at any given time.

Overview of ReplicaSets

A ReplicaSet is a process that runs multiple instances of a pod and keeps the specified number of pods constant. It makes sure that a stable set of replica pods is running at any given time, which guarantees an available specified number of identical pods.

When a pod fails, a ReplicaSet brings up a new instance of the pod and scales up when the running instances reach a specified number. Conversely, it scales down or deletes pods when an instance with the same label is created.

Create a ReplicaSet

Use the kubectl create and kubectl apply commands to create ReplicaSets. The following example creates a ReplicaSet using a YAML file:

kubectl apply –f nginx_replicaset.yaml

The features of a ReplicaSet configuration file are shown in YAML format:

apiVersion: apps/v1  
kind: ReplicaSet  
metadata: 
      name: web
      labels: 
         env: dev
         role: web
spec:  
   replicas: 4
   selector: 
       matchlabels: 
       role: web
        template:
           metadata:
       labels:
           role: web
spec:  
      containers:  
           -name: nginx  
           image: nginx

After you create a ReplicaSet, you can view the status by running the following command:

kubectl get rs

You can remove, but not delete, a pod that a ReplicaSet manages by changing its label using the kubectl edit command. For example, if you run kubectl edit pods 7677-69h5b, you can change the pod label once the configuration file opens.

Scale a ReplicaSet

There are two ways to change the number of pods that a ReplicaSet manages.

  • Edit the controller's configuration using the following command:

    kubectl edit rs <ReplicaSet_NAME>

  • Directly increase or decrease the number using the following command:

kubectl scale –replicas=2 rs <ReplicaSet_NAME>

When you edit a manifest file, you can replace your existing configuration with the updated one:

kubectl replace –f nginx_replicaset.yaml

Then, to view the status of your ReplicaSet, run kubectl get rs <ReplicaSet_NAME>.

Autoscaling is also an option with ReplicaSets using kubectl autoscale rs web –max=5. You can use autoscaling to adapt the number of pods according to the CPU load of a node.

Delete a ReplicaSet

As with other Kubernetes objects, such as DaemonSets, you can delete ReplicaSets using the kubectl delete command. For example, you can use the following commands:

  • To delete a ReplicaSet using the ReplicaSet name, run the following command:

    kubectl delete rs <ReplicaSet_NAME>

  • To delete a ReplicaSet using its filename, run the following command:

    kubectl delete –f nginx_replicaset.yaml

  • The preceding commands delete the ReplicaSet and all the pods that it manages. If you want to delete only the ReplicaSet resource, and keep the pods without an owner, you need to manually delete them. To manually delete a ReplicaSet, run the following command:

    kubectl delete rs <ReplicaSet_NAME> --cascade=false

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