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In this lesson, you will learn how to create a Kubernetes Deployment using a configuration similar to a ReplicaSet definition. Follow these steps to create a Deployment, starting from setting up the necessary files to verifying the deployment status in your cluster.

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Step 1: Set Up Your Project Directory

Create a new folder called Deployments within your project directory. Then, inside the Deployments folder, create a file named deployment.yaml.
Using a split editor can help you compare the new deployment file with your existing ReplicaSet definition side by side.

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Step 2: Base Your Deployment on the ReplicaSet Definition

Locate your existing ReplicaSet.yaml file and open it in a split view with your new deployment.yaml file. This approach lets you reference the ReplicaSet configuration while you build your Deployment. Begin your deployment.yaml file by specifying the API version and kind. Since the ReplicaSet uses apps/v1, you will use the same API version, but change the kind to Deployment: 
apiVersion: apps/v1
kind: Deployment

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Step 3: Define Metadata

Next, add metadata details for your deployment. For example, set the deployment name to myapp-deployment and include labels to help categorize and identify the deployment: 
metadata:
  name: myapp-deployment
  labels:
    tier: frontend
    app: nginx

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Step 4: Configure the Spec Section

The specification section of the deployment is very similar to the ReplicaSet’s. You can copy the spec section from ReplicaSet.yaml and modify it as necessary. In this example, update the replica count to three: 
spec:
  selector:
    matchLabels:
      app: myapp
  replicas: 3
  template:
    metadata:
      name: nginx-2
      labels:
        app: myapp
    spec:
      containers:
        - name: nginx
          image: nginx
For reference, here is the original ReplicaSet.yaml content that served as a starting point: 
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: myapp-replicaset
  labels:
    app: myapp
spec:
  selector:
    matchLabels:
      app: myapp
  replicas: 4
  template:
    metadata:
      name: nginx-2
      labels:
        app: myapp
    spec:
      containers:
        - name: nginx
          image: nginx

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Step 5: Deploy Your Configuration

After saving your changes to deployment.yaml, open your terminal, navigate to the project’s root directory, and confirm that the Deployments directory exists. To create the deployment, run the following command using kubectl with the -f flag to specify your deployment file: 
kubectl create -f deployment.yaml
Once the command completes, verify the deployment’s status with: 
kubectl get deployments
You should see output indicating that the deployment is running with three available Pods, similar to the following: 
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
myapp-deployment    3/3     3            3           10s

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Step 6: Verify the Pods and Deployment Details

To view the Pods created by the ReplicaSet for this deployment, execute: 
kubectl get pods
The output will list the three running Pods, for example: 
NAME                     READY   STATUS    RESTARTS   AGE
myapp-replicaset-pjs89   1/1     Running   0          34m
myapp-replicaset-pwv6h   1/1     Running   0          34m
myapp-replicaset-zr6c7   1/1     Running   0          23s
Next, inspect the details of your deployment by running: 
kubectl describe deployment myapp-deployment
This command provides comprehensive information, including the deployment’s name, namespace, labels, POD template details, and scaling events indicating that three Pods are ready.

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Step 7: List All Kubernetes Objects

To view all objects created in your cluster, run the following command: 
kubectl get all
This will display the deployment, its corresponding ReplicaSet (named myapp-replicaset), and the three Pods managed by the ReplicaSet.
This lesson has guided you through creating a Kubernetes Deployment from a ReplicaSet template, deploying it using kubectl, and verifying the deployment along with its associated Pods.

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