Create and Manage Deployment Using Declarative Approach¶

Let's see how you can create and manage Kubernetes Deployments declaratively.

Here is the Docker Image used in this tutorial: reyanshkharga/nginx

Step 1: Create Deployment Manifest¶

First, we need to write the Deployment manifest as follows:

my-deployment.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
        tier: backend
    spec:
      containers:
      - name: nginx
        image: reyanshkharga/nginx:v1
        imagePullPolicy: Always
        ports:
          - containerPort: 80

Required fields:

apiVersion - Which version of the Kubernetes API you're using to create this object.
kind - What kind of object you want to create.
metadata - Data that helps uniquely identify the object, including a name string, UID , and optional namespace.
spec - What state you desire for the object.

You'll notice that the YAML configuration for the Deployment looks very similar to the ReplicaSet, with the exception of the kind attribute.

Step 2: Create Deployment¶

Let's use kubectl apply to apply the manifest and create the Deployment:

# Create deployment
kubectl apply -f my-deployment.yml

Step 3: List Deployments¶

List Deployments and verify that the deployment we created is available:

kubectl get deployments

Step 4: View ReplicaSets Created by the Deployment¶

As discussion earlier, when you create a Deployment, kubernetes creates a ReplicaSet for you and manages the replicas of your application based on the Deployment's desired state.

Let's list the ReplicaSets created by my-deployment:

kubectl get rs | grep my-deployment

You'll see a ReplicaSet created and managed by the Deployment.

The name of the ReplicaSets created by Deployments starts with the deployment name.

Step 5: View Pods Created by the Deployment¶

List pods:

kubectl get pods

You'll see pods created and managed by the Deployment.

The name of the pods created by Deployments starts with the deployment name.

Step 6: Describe the Deployment¶

Describe the deployment:

kubectl describe deployment/my-deployment
{OR}
kubectl describe deployment my-deployment

Step 7: Scale the Deployment¶

Let's scale replicas to 3:

kubectl scale deployment/my-deployment --replicas 3

You can also use kubectl edit command to scale the Deployment as follows:

Set the editor you want to use (Default is vim):

export KUBE_EDITOR=nano

Edit the YAML manifest by changing the value of replicas to a desired value and then save file to scale the deployment:

kubectl edit deployment/my-deployment
{OR}
kubectl edit deployment my-deployment

Verify that the deployment was scaled:

# List deployments
kubectl get deployments

# List replicasets
kubectl get rs | grep my-deployment

# List pods
kubectl get pods | grep my-deployment

Step 8: Update the Deployment¶

Let's update the deployment to use a new image reyanshkharga/nginx:v2.

In the Deployment YAML manifest change the value of image to reyanshkharga/nginx:v2.

Now, apply the manifest to update the deployment:

kubectl apply -f my-deployment.yml

Step 9: Verify if the Deployment Was Updated¶

Verfify the Deployment, Pods, and ReplicaSets:

# Describe deployment
kubectl describe deploy/my-deployment

# List pods created by the deployment
kubectl get pods | grep my-deployment

# List replicasets created by the deployment
kubectl get rs | grep my-deployment

You'll notice the following:

The Deployment is updated and uses the updated image.
A new ReplicaSet is created
New Pods come up and old Pods are terminated.
Old ReplicaSets are not deleted (unless this was 11th revision)

Here's a visual representation of the rolling update described above:

Step 10: Update the Deployment Few More Times¶

Change the image to reyanshkharga/nginx:v3 and apply the configuration again.
Change the image to reyanshkharga/nginx:v4 and apply the configuration again.

Step 11: List Deployment Revisions¶

As discussed earlier, Kubernetes Deployment controller stores up to 10 revisions of a Deployment.

You can configure the maximum number of revisions to keep by setting the .spec.revisionHistoryLimit field in the Deployment's YAML file.

List the Deployment revisions:

kubectl rollout history deployment/my-deployment

Get the details of a particular revision:

kubectl rollout history deployment/my-deployment --revision=2

List ReplicaSets managed by the Deployment:

kubectl get rs | grep my-deployment

Step 12: Rollback the Deployment¶

Rollback to the previous version:

kubectl rollout undo deployment/my-deployment

Verify rollback:

kubectl get rs | grep my-deployment

You'll notice that the pods are now managed by the replicaset from previous revision.

You can also rollback to a particular version as follows:

kubectl rollout undo deployment my-deployment --to-revision=1

Verify rollback:

kubectl get rs | grep my-deployment

Here's a visual representation of the rollback flow described above:

Step 13: Delete the Deployment¶

kubectl delete deployment/my-deployment
{OR}
kubectl delete -f my-deployment.yml

References: