> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Solution ReplicaSets optional > This lab explores ReplicaSets in Kubernetes, covering verification, troubleshooting, scaling, and modifying ReplicaSets through practical commands and configurations. In this lab, we explore ReplicaSets in Kubernetes. Follow along as we review lab steps, execute commands, and troubleshoot issues. This guide covers checking current resources, examining ReplicaSet configurations, troubleshooting image pull errors, scaling, and modifying ReplicaSets using definition files. *** ## 1. Verify Existing Pods Begin by checking the current pods in your cluster. Run the following command: ```bash theme={null} kubectl get pods ``` The result is expected to be: ```plaintext theme={null} No resources found in default namespace. ``` This indicates that there are no pods currently running. *** ## 2. Review Existing ReplicaSets Next, inspect if any ReplicaSets are present: ```bash theme={null} kubectl get replicaset ``` Initially, no ReplicaSets are available. After making configuration changes, a new ReplicaSet may be created. Check its details using the same command: ```bash theme={null} kubectl get replicaset ``` You might see an output similar to: ```plaintext theme={null} NAME DESIRED CURRENT READY AGE new-replica-set 4 4 0 9s ``` *** ## 3. Analyze ReplicaSet Details To obtain a detailed description of the ReplicaSet, execute: ```bash theme={null} kubectl describe replicaset new-replica-set ``` Focus on the pod template section; observe the container configuration: * **Image:** `busybox777` * **Command:** ```bash theme={null} sh -c "echo Hello Kubernetes! && sleep 3600" ``` Below is an excerpt from the output: ```bash theme={null} Name: new-replica-set Namespace: default Selector: name=busybox-pod Labels: Annotations: Replicas: 4 current / 4 desired Pods Status: 0 Running / 4 Waiting / 0 Succeeded / 0 Failed Pod Template: Labels: name=busybox-pod Containers: busybox-container: Image: busybox777 Port: Host Port: Command: sh -c echo Hello Kubernetes! && sleep 3600 Mounts: Volumes: Events: Type Reason Age From Message Normal SuccessfulCreate 60s replicaset-controller Created pod: new-replica-set-7r2qw Normal SuccessfulCreate 60s replicaset-controller Created pod: new-replica-set-wkzjh Normal SuccessfulCreate 60s replicaset-controller Created pod: new-replica-set-tn2mp Normal SuccessfulCreate 60s replicaset-controller Created pod: new-replica-set-vpkh8 ``` The configuration reveals that the pods are configured to run the image `busybox777`. *** ## 4. Check Pod Readiness Examine the number of ready pods in the ReplicaSet. As seen from the detailed description: ```bash theme={null} Pods Status: 0 Running / 4 Waiting / 0 Succeeded / 0 Failed ``` This indicates that none of the pods are ready at this point. *** ## 5. Troubleshoot Pod Readiness Issues Investigate why the pods are not transitioning to a ready state by describing one of them: ```bash theme={null} kubectl describe pod new-replica-set-7r2qw ``` The output shows that the pod is in a waiting state with the reason `ImagePullBackOff`. This error occurs because the image `busybox777` cannot be pulled, likely due to a non-existent repository or missing authorization. An excerpt from the pod events: ```plaintext theme={null} State: Waiting Reason: ImagePullBackOff ... Events: Normal Pulling ... kubelet Pulling image "busybox777" Warning Failed ... kubelet Failed to pull image "busybox777": pull access denied, repository does not exist or may require authorization... ``` Kubernetes is unable to pull the image "busybox777" because it either does not exist or you might need to provide proper credentials. *** ## 6. Delete a Pod and Observe ReplicaSet Self-Healing To demonstrate the self-healing nature of ReplicaSets, delete one of the pods. First, list all pods: ```bash theme={null} kubectl get pods ``` You may see output such as: ```plaintext theme={null} NAME READY STATUS RESTARTS AGE new-replica-set-wkzjh 0/1 ImagePullBackOff 0 2m59s new-replica-set-vpkh8 0/1 ImagePullBackOff 0 2m59s new-replica-set-7r2qw 0/1 ImagePullBackOff 0 2m59s new-replica-set-tn2mp 0/1 ImagePullBackOff 0 2m59s ``` Delete one pod: ```bash theme={null} kubectl delete pod new-replica-set-wkzjh ``` The system confirms deletion: ```plaintext theme={null} pod "new-replica-set-wkzjh" deleted ``` After deletion, list the pods again: ```bash theme={null} kubectl get pods ``` A new pod will be created automatically by the ReplicaSet to maintain the desired count. Notice that the new pod has a different name and age compared to the existing ones. *** ## 7. Create a ReplicaSet Using a Definition File Now, learn how to create a ReplicaSet from a YAML definition file. First, confirm the existence of the file: ```bash theme={null} ls /root ``` Assuming you see a file named `ReplicaSet definition.yaml`, attempt to create the ReplicaSet: ```bash theme={null} kubectl create -f /root/ReplicaSet\ definition.yaml ``` If an error similar to the following is returned: ```plaintext theme={null} no matches for kind "ReplicaSet" in version "v1" ``` This indicates that the API version in the file is incorrect. The proper API version for ReplicaSets is `apps/v1`. Use the command `kubectl explain replicaset` to verify the correct API version. Update the file with the correct API version and create it again. *** ## 8. Correct a Second ReplicaSet Definition File Attempt to create a second ReplicaSet using another definition file: ```bash theme={null} kubectl create -f replicaset-definition-2.yaml ``` If you encounter this error: ```plaintext theme={null} The ReplicaSet "replicaset-2" is invalid: spec.template.metadata.labels: Invalid value: map[string]string{"tier":"nginx"}: selector does not match template labels ``` Open the file for editing: ```bash theme={null} vi replicaset-definition-2.yaml ``` Examine the `spec.selector.matchLabels` and `template.metadata.labels` sections. They must match exactly. For example: ```yaml theme={null} apiVersion: apps/v1 kind: ReplicaSet metadata: name: replicaset-2 spec: replicas: 2 selector: matchLabels: tier: nginx template: metadata: labels: tier: nginx spec: containers: - name: nginx image: nginx ``` After ensuring both fields match, save the file and run: ```bash theme={null} kubectl create -f replicaset-definition-2.yaml ``` Verify the creation of all ReplicaSets: ```bash theme={null} kubectl get rs ``` Expected output: ```plaintext theme={null} NAME DESIRED CURRENT READY AGE new-replica-set 4 4 0 10m replicaset-1 2 2 2 3m4s replicaset-2 2 2 2 22s ``` If necessary, delete the extra ReplicaSets: ```bash theme={null} kubectl delete rs replicaset-1 kubectl delete rs replicaset-2 ``` *** ## 9. Update the Original ReplicaSet Image The original ReplicaSet is still configured to use `busybox777`. To update the image to `busybox`, edit the ReplicaSet: ```bash theme={null} kubectl edit rs new-replica-set ``` Locate the container section and change: ```yaml theme={null} image: busybox777 ``` to ```yaml theme={null} image: busybox ``` Save the changes and exit the editor. Bear in mind that updating the ReplicaSet does not automatically update the running pods; you must delete the existing pods so the ReplicaSet can recreate them with the correct image. List the pods: ```bash theme={null} kubectl get pods ``` Then, delete the current pods: ```bash theme={null} kubectl delete pod new-replica-set-vpkh8 new-replica-set-tn2mp new-replica-set-7r2qw new-replica-set-hcmbw ``` After deletion, new pods will be created. Verify that they are transitioning from "ContainerCreating" to "Running": ```bash theme={null} kubectl get pods ``` *** ## 10. Scaling the ReplicaSet ### Scale Up to 5 Pods Increase the ReplicaSet to five pods with the scale command: ```bash theme={null} kubectl scale rs new-replica-set --replicas=5 ``` Verify the scale-up by listing the pods again: ```bash theme={null} kubectl get pods ``` ### Scale Down to 2 Pods To reduce the number of pods to two, edit the ReplicaSet: ```bash theme={null} kubectl edit rs new-replica-set ``` Update the `spec.replicas` field to 2 and save the file. The ReplicaSet will automatically adjust the pod count accordingly. *** This concludes the ReplicaSets lab. In the next lesson, we will explore Deployments and demonstrate how they extend the concepts introduced by ReplicaSets. For more details on Kubernetes concepts, visit the [Kubernetes Documentation](https://kubernetes.io/docs/).