> ## 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. # Lab Solution ReplicaSets optional > Step-by-step ReplicaSet lab solution demonstrating Kubernetes ReplicaSet behavior, debugging commands, common errors and fixes including image pull, API version, selector mismatches, scaling and pod recreation This lesson walks through the ReplicaSet lab solution step-by-step, preserving the lab question order and showing the exact commands and sample outputs used to inspect and fix the resources. Use this as a reference to understand ReplicaSet behavior, debugging steps, and common fixes. Quick reference - common commands: | Action | Command | | - | - | | List pods | `kubectl get pods` | | List ReplicaSets | `kubectl get replicaset` or `kubectl get rs` | | Describe ReplicaSet | `kubectl describe replicaset ` | | Describe Pod | `kubectl describe pod ` | | Create from file | `kubectl create -f ` | | Edit resource | `kubectl edit rs ` | | Scale ReplicaSet | `kubectl scale rs --replicas=` | | Watch pods | `kubectl get pods --watch` | *** ## 1) How many pods exist on the system? Run: ```bash theme={null} kubectl get pods ``` Initial output: ```console theme={null} No resources found in default namespace. ``` Conclusion: there are 0 pods initially. *** ## 2) How many ReplicaSets exist on the system? Run: ```bash theme={null} kubectl get replicaset ``` Initial output: ```console theme={null} No resources found in default namespace. ``` Conclusion: there are 0 ReplicaSets initially. Later, after a ReplicaSet is created, it can be observed: ```bash theme={null} kubectl get replicaset ``` Example output: ```console theme={null} NAME DESIRED CURRENT READY AGE new-replica-set 4 4 0 9s ``` *** ## 3) What is the desired number of pods in the new ReplicaSet? From the `kubectl get replicaset` output: * Desired = 4 Answer: 4 *** ## 4) What image is used to create the pods in the new ReplicaSet? To inspect the ReplicaSet template: ```bash theme={null} kubectl describe replicaset new-replica-set ``` Relevant excerpt: ```console theme={null} Name: new-replica-set Namespace: default Selector: name=busybox-pod 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 Command: sh -c echo Hello Kubernetes! && sleep 3600 Events: 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 ``` From the pod template, the image is `busybox777`. Answer: `busybox777` *** ## 5) How many pods are Ready in the new ReplicaSet? From the `kubectl get replicaset` / `kubectl describe` output: * Ready = 0 So none of the pods are Ready. *** ## 6) Why are the pods not Ready? Inspect a failing pod to find the root cause: ```bash theme={null} kubectl describe pod new-replica-set-7r2qw ``` Relevant excerpt: ```console theme={null} Containers: busybox-container: Command: sh -c echo Hello Kubernetes! && sleep 3600 State: Waiting Reason: ImagePullBackOff Ready: False Restart Count: 0 Events: Normal Scheduled 2m23s default-scheduler Successfully assigned default/new-replica-set-7r2qw to controlplane Normal Pulling 46s (x4 over 2m23s) kubelet Pulling image "busybox777" Warning Failed 46s (x4 over 2m22s) kubelet Failed to pull image "busybox777": rpc error: code = Unknown desc = failed to pull and unpack image "docker.io/library/busybox777:latest": failed to resolve reference "docker.io/library/busybox777:latest": pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed Warning Failed 34s (x6 over 2m21s) kubelet Error: ImagePullBackOff Normal BackOff 23s (x7 over 2m21s) kubelet Back-off pulling image "busybox777" ``` Reason: the kubelet cannot pull image `busybox777` — the repository does not exist (invalid image name), causing ImagePullBackOff. Therefore pods are not Ready. *** ## 7) Delete a pod from the ReplicaSet and observe behavior Delete one pod: ```bash theme={null} kubectl delete pod new-replica-set-wkzjh ``` Then list pods: ```bash theme={null} kubectl get pods ``` Example output after deletion: ```console theme={null} NAME READY STATUS RESTARTS AGE new-replica-set-hcmbw 0/1 ErrImagePull 0 17s new-replica-set-vpkh8 0/1 ErrImagePull 0 3m26s new-replica-set-7r2qw 0/1 ErrImagePull 0 3m26s new-replica-set-tn2mp 0/1 ErrImagePull 0 3m26s ``` Explanation: Deleting a pod managed by a ReplicaSet causes the ReplicaSet controller to immediately create a replacement to maintain the desired count. That's why you still see four pods even after deleting one. *** ## 8) Create a ReplicaSet from a definition file and fix apiVersion issue List files in `/root`: ```bash theme={null} ls /root # replicaset-definition-1.yaml replicaset-definition-2.yaml sample.yaml ``` Attempt to create the first definition: ```bash theme={null} kubectl create -f /root/replicaset-definition-1.yaml ``` Error: ```console theme={null} error: unable to recognize "/root/replicaset-definition-1.yaml": no matches for kind "ReplicaSet" in version "v1" ``` Inspect the file: ```yaml theme={null} # /root/replicaset-definition-1.yaml apiVersion: v1 kind: ReplicaSet metadata: name: replicaset-1 spec: replicas: 2 selector: matchLabels: tier: frontend template: metadata: labels: tier: frontend spec: containers: - name: nginx image: nginx ``` Problem: `apiVersion` is set to `v1` but ReplicaSet is in the `apps` API group (`apps/v1`). Discover the correct API with: ```bash theme={null} kubectl explain replicaset ``` Fix the file by updating `apiVersion` to `apps/v1`, then create it: ```bash theme={null} # Update apiVersion to apps/v1 in replicaset-definition-1.yaml kubectl create -f /root/replicaset-definition-1.yaml ``` Success: ```console theme={null} replicaset.apps/replicaset-1 created ``` ReplicaSet belongs to the `apps` API group. Always use `apiVersion: apps/v1`. Use `kubectl explain ` to discover the correct API version and available fields. *** ## 9) Fix the second definition file: selector vs template labels Attempt to create the second file: ```bash theme={null} kubectl create -f replicaset-definition-2.yaml ``` Error: ```console 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` ``` Inspect `replicaset-definition-2.yaml` (excerpt): ```yaml theme={null} apiVersion: apps/v1 kind: ReplicaSet metadata: name: replicaset-2 spec: replicas: 2 selector: matchLabels: tier: frontend template: metadata: labels: tier: nginx spec: containers: - name: nginx image: nginx ``` Problem: `spec.selector.matchLabels` is `tier: frontend` while the Pod template labels are `tier: nginx`. A ReplicaSet's selector must match the Pod template labels so it can manage the created pods. Fix: make `selector.matchLabels` and `template.metadata.labels` match (for example, set both to `tier: frontend`), then create: ```bash theme={null} kubectl create -f replicaset-definition-2.yaml ``` Success: ```console theme={null} replicaset.apps/replicaset-2 created ``` Check ReplicaSets: ```bash theme={null} kubectl get rs ``` Example output: ```console 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 ``` *** ## 10) Delete replicaset-1 and replicaset-2 Delete both ReplicaSets: ```bash theme={null} kubectl delete rs replicaset-1 replicaset-2 ``` Output: ```console theme={null} replicaset.apps "replicaset-1" deleted replicaset.apps "replicaset-2" deleted ``` *** ## 11) Fix the original ReplicaSet to use the correct busybox image The `new-replica-set` still references the invalid image `busybox777`. Edit the ReplicaSet to correct the container image: ```bash theme={null} kubectl edit rs new-replica-set ``` In the editor, change the container image from `busybox777` to `busybox`. Example edited snippet: ```yaml theme={null} spec: replicas: 4 selector: matchLabels: name: busybox-pod template: metadata: labels: name: busybox-pod spec: containers: - command: - sh - -c - echo Hello Kubernetes! && sleep 3600 image: busybox imagePullPolicy: Always name: busybox-container ``` Save the change. The ReplicaSet object is updated, but existing pods do not automatically get replaced just because the ReplicaSet pod template changed. Editing a ReplicaSet's pod template updates the ReplicaSet object, but it does not replace existing pods. To apply the new template to running pods, either delete the existing pods (so the ReplicaSet recreates them) or recreate the ReplicaSet. *** ## 12) Recreate pods to pick up the new image Delete the ReplicaSet's pods so the controller will create new pods using the corrected image: ```bash theme={null} kubectl delete pod new-replica-set-vpkh8 new-replica-set-tn2mp new-replica-set-7r2qw new-replica-set-hcmbw ``` Watch pods being recreated: ```bash theme={null} kubectl get pods --watch ``` Sample outputs as pods are created and become Running: ```console theme={null} NAME READY STATUS RESTARTS AGE new-replica-set-8z7z5 0/1 ContainerCreating 0 12s new-replica-set-f5gth 0/1 ContainerCreating 0 12s new-replica-set-nsbgx 0/1 ContainerCreating 0 12s new-replica-set-whhll 0/1 ContainerCreating 0 12s # A short while later NAME READY STATUS RESTARTS AGE new-replica-set-f5gth 1/1 Running 0 18s new-replica-set-nsbgx 1/1 Running 0 18s new-replica-set-8z7z5 1/1 Running 0 18s new-replica-set-whhll 1/1 Running 0 18s ``` Verify ReplicaSet ready pods: ```bash theme={null} kubectl get rs ``` Example output: ```console theme={null} NAME DESIRED CURRENT READY AGE new-replica-set 4 4 4 15m ``` Now the pods are running with the corrected `busybox` image. Note: When you change a ReplicaSet's pod template, existing pods are not automatically replaced. Deleting the pods causes the ReplicaSet to recreate them with the new template. *** ## 13) Scale the ReplicaSet to 5 pods Scale with `kubectl scale`: ```bash theme={null} kubectl scale rs new-replica-set --replicas=5 ``` Confirm: ```bash theme={null} kubectl get pods ``` Example output: ```console theme={null} NAME READY STATUS RESTARTS AGE new-replica-set-f5gth 1/1 Running 0 55s new-replica-set-nsbgx 1/1 Running 0 55s new-replica-set-8z7z5 1/1 Running 0 55s new-replica-set-whhll 1/1 Running 0 55s new-replica-set-mwpnz 1/1 Running 0 4s ``` You can also edit the ReplicaSet and modify `spec.replicas` to scale. *** ## 14) Scale the ReplicaSet down to 2 pods (edit approach) Edit the ReplicaSet: ```bash theme={null} kubectl edit rs new-replica-set ``` Change `spec.replicas` to `2`: ```yaml theme={null} spec: replicas: 2 selector: matchLabels: name: busybox-pod template: metadata: labels: name: busybox-pod ... ``` Save the change. The ReplicaSet controller will terminate excess pods to match the desired replica count of 2. *** That's it for this lab lesson. Links and References * [Kubernetes ReplicaSet documentation](https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/) * [kubectl reference](https://kubernetes.io/docs/reference/kubectl/) * [kubectl explain](https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#explain) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.