Solution Deployments optional

In this lab article, you will be introduced to Kubernetes deployments. We will walk through each step of the process while ensuring that your cluster is correctly set up and that deployments function as expected.

Step 1: Check the Initial Cluster State

Before creating any deployments, verify that your cluster has no existing pods, ReplicaSets, or deployments.

Start by checking for pods:

controlplane ~ ➜ kubectl get pods
No resources found in default namespace.

Then, check for ReplicaSets:

controlplane ~ ➜ kubectl get rs
No resources found in default namespace.

Finally, check for any deployments:

controlplane ~ ➜ kubectl get deployments
No resources found in default namespace.

At this point, your environment is clean with zero pods, zero ReplicaSets, and zero deployments.

Step 2: Observe Changes After a Deployment is Created

After applying some changes, check the deployments again. You should now see that one deployment exists:

controlplane ~ ➜ kubectl get deployments
NAME                  READY   UP-TO-DATE   AVAILABLE   AGE
frontend-deployment   0/4     4            0           10s

Examine the ReplicaSet created by that deployment:

controlplane ~ ➜ kubectl get rs
NAME                                   DESIRED   CURRENT   READY   AGE
frontend-deployment-7f8dcd-b696        4         4         0       35s

And then inspect the pods:

controlplane ~ ➜ kubectl get pods
NAME                                             READY   STATUS             RESTARTS   AGE
frontend-deployment-7f8dcd-b696-stmbx            0/1     ImagePullBackOff   0          59s
frontend-deployment-7f8dcd-b696-zc6x             0/1     ErrImagePull       0          59s
frontend-deployment-7f8dcd-b696-jgcbx            0/1     ErrImagePull       0          59s
frontend-deployment-7f8dcd-b696-jbr44            0/1     ErrImagePull       0          59s

Because none of the four pods are in a ready state, you need to identify which image they are trying to pull. Run the following command to display detailed information for one pod:

kubectl describe pod frontend-deployment-7fd8cdb696-stmbx

From the output, notice that the specified image is busybox:888. Since this image does not exist, the pods are unable to reach a ready state.

Step 3: Create a New Deployment Using a YAML Definition

Verify Your Current Directory and Files

Ensure you are in the correct working directory and check the available files:

controlplane ~ ➜ pwd
/root

controlplane ~ ➜ ls
deployment-definition-1.yaml  sample.yaml

Attempt to Create the Deployment

Run the following command to create the deployment from the YAML file:

controlplane ~ ➜ kubectl create -f deployment-definition-1.yaml

If you encounter an error such as:

Error from server (BadRequest): error when creating "deployment-definition-1.yaml": deployment in version "v1" cannot be handled as a Deployment: no kind "deployment" is registered for version "apps/v1" in scheme "k8s.io/apimachinery/v1.23.3-k3s1/pkg/runtime/scheme.go:100"

Open the file to correct the issue:

controlplane ~ ➜ vi deployment-definition-1.yaml

Update the Deployment YAML

The error is caused by incorrect casing in the kind field. The resource kind should be capitalized. Use the corrected YAML below:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-1
spec:
  replicas: 2
  selector:
    matchLabels:
      name: busybox-pod
  template:
    metadata:
      labels:
        name: busybox-pod
    spec:
      containers:
      - name: busybox-container
        image: busybox888
        command:
        - sh
        - "-c"
        - echo Hello Kubernetes! && sleep 3600

After saving the changes, create the deployment again:

controlplane ~ ➜ kubectl create -f deployment-definition-1.yaml

Step 4: Create a Deployment Using Command-Line Parameters

You can also create a deployment by specifying parameters directly in the command line. First, review the help for deployment creation:

kubectl create deployment --help

For example, to create a deployment named http-frontend using a specified image with three replicas, run:

kubectl create deployment http-frontend --image=<your-image> --replicas=3

After executing the command, verify that the deployment and pods are running as expected:

kubectl get deployments

Make sure that the http-frontend deployment reflects the desired number of replicas in the ready state.

Final Validation

To ensure all deployments are functioning, validate by checking that all created deployments are running and the pods are in a ready state. This confirms that your environment is correctly configured and operational.

This concludes the lab article on Kubernetes deployments. In upcoming labs, you’ll explore additional Kubernetes functionalities to further enhance your skills.

Links and References

• Kubernetes Documentation
• Kubernetes Basics
• Docker Hub
• Terraform Registry