Deployments are a key feature in Kubernetes that provide declarative updates to applications. They manage the creation and scaling of Pods, ensuring that the desired state of the application is maintained. This section will cover the basics of Deployments, how to create and manage them, and practical examples to solidify your understanding.

• Deployment: A resource object in Kubernetes that provides declarative updates to applications.
• ReplicaSet: Ensures a specified number of pod replicas are running at any given time.
• Pod Template: Describes the pods that will be created by the Deployment.

A Deployment is defined using a YAML file. Below is an example of a simple Deployment YAML file:

• apiVersion: Specifies the API version (apps/v1).
• kind: Specifies the type of resource (Deployment).
• metadata: Contains the name of the Deployment.
• spec: Defines the desired state of the Deployment.
  • replicas: Number of pod replicas to run.
  • selector: Identifies the pods managed by the Deployment.
  • template: Describes the pods to be created.
    • metadata: Labels for the pods.
    • spec: Defines the containers within the pods.
      • containers: List of containers to run in the pod.
        • name: Name of the container.
        • image: Docker image to use.
        • ports: Ports to expose.

To create a Deployment, use the kubectl apply command:

To view the status of the Deployment, use the kubectl get command:

To update a Deployment, modify the YAML file and apply the changes:

To scale a Deployment, use the kubectl scale command:

Kubernetes supports rolling updates to Deployments, allowing you to update the pods without downtime. Modify the image in the YAML file and apply the changes:

Apply the changes:

To rollback to a previous version, use the kubectl rollout undo command:

1. Create a Deployment:

   • Write a YAML file for a Deployment that runs an Nginx server with 3 replicas.
   • Apply the Deployment using kubectl apply.

2. Update the Deployment:

   • Change the Nginx image version in the YAML file.
   • Apply the changes and observe the rolling update.

3. Scale the Deployment:

   • Scale the Deployment to 5 replicas using kubectl scale.

4. Rollback the Deployment:

   • Rollback to the previous version using kubectl rollout undo.

1. Create a Deployment:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: nginx-deployment
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: nginx
     template:
       metadata:
         labels:
           app: nginx
       spec:
         containers:
         - name: nginx
           image: nginx:1.14.2
           ports:
           - containerPort: 80
   

   Apply the Deployment:

   kubectl apply -f nginx-deployment.yaml
   

2. Update the Deployment: Change the image version in the YAML file:

   spec:
     containers:
     - name: nginx
       image: nginx:1.16.0
   

   Apply the changes:

   kubectl apply -f nginx-deployment.yaml
   

3. Scale the Deployment:

   kubectl scale deployment/nginx-deployment --replicas=5
   

4. Rollback the Deployment:

   kubectl rollout undo deployment/nginx-deployment
   

In this section, you learned about Kubernetes Deployments, how to create and manage them, and how to perform updates and rollbacks. Deployments are a powerful feature that ensures your applications run reliably and can be updated without downtime. In the next section, we will explore Services, which allow you to expose your applications to the network.