Using the Deployment object, we can perform rolling updates of the application seamlessly (Zero downtime for the applications). In real-world applications, you do not create a Pod and ReplicaSet definition file. You create a deployment definition file only, which in turn create replica sets and Pods

Let’s create a deployment.

Step 1: Create ‘employeeServiceDeployment.yml’ file.

employeeServiceDeployment.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: employee-service-deployment
  labels:
    app: employee-service-deployment
    author: krishna
    serviceType: webservice
spec:
  template:
    metadata:
      name: employee-service
      labels:
        app: employee-service
        author: krishna
        serviceType: webservice
    spec:
      containers:
      - name: employee-service-container
        image: jboss/wildfly

  replicas: 5
  selector:
    matchLabels:
      app: employee-service

template:

It has the Pod specification.

replicas: 5

Specifies the number of copies of Pod to run. Here 5 Pods of the application ‘jboss/wildfly’ will run.

selector:

    matchLabels:

      app: employee-service

Kubernetes use matchLabels to identify how labels are identified against a Pod.

Step 2: Create a deployment from the definition file.

$kubectl create -f employeeServiceDeployment.yml 
deployment.apps/employee-service-deployment created

Step 3: List all the deployments.

$kubectl get deployments
NAME                          READY   UP-TO-DATE   AVAILABLE   AGE
employee-service-deployment   3/5     5            3           15s

As you see the output, deployment with name ‘employee-service-deployment’ is created and 3 Pods out of 5 are up and running.

Wait for some time and list deployments again. You will see that all the Pods are up and running.

$kubectl get deployments
NAME                          READY   UP-TO-DATE   AVAILABLE   AGE
employee-service-deployment   5/5     5            5           72s

Deployment automatically creates a replicaset. To confirm this, list all the replicasets.

$kubectl get replicaset
NAME                                    DESIRED   CURRENT   READY   AGE
employee-service-deployment-dff6c9cdf   5         5         5       3m15s

Query Pods.

$kubectl get pods
NAME                                          READY   STATUS    RESTARTS   AGE
employee-service-deployment-dff6c9cdf-2wrg9   1/1     Running   0          2m6s
employee-service-deployment-dff6c9cdf-8m7cr   1/1     Running   0          2m6s
employee-service-deployment-dff6c9cdf-kv9ck   1/1     Running   0          2m6s
employee-service-deployment-dff6c9cdf-pbfpr   1/1     Running   0          2m6s
employee-service-deployment-dff6c9cdf-s4nh4   1/1     Running   0          2m6s

Step 4: To know more information about the deployment, execute the command ‘kubectl describe deployment’.

$kubectl describe deployment
Name:                   employee-service-deployment
Namespace:              default
CreationTimestamp:      Fri, 05 Jun 2020 00:02:53 +0530
Labels:                 app=employee-service-deployment
                        author=krishna
                        serviceType=webservice
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=employee-service
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=employee-service
           author=krishna
           serviceType=webservice
  Containers:
   employee-service-container:
    Image:        jboss/wildfly
    Port:         
    Host Port:    
    Environment:  
    Mounts:       
  Volumes:        
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
  Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  
NewReplicaSet:   employee-service-deployment-dff6c9cdf (5/5 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  11m   deployment-controller  Scaled up replica set employee-service-deployment-dff6c9cdf to 5

Step 5: You can delete a deployment by executing the below command.

kubectl delete deployment {deploymentName}

$kubectl get deployment
NAME                          READY   UP-TO-DATE   AVAILABLE   AGE
employee-service-deployment   5/5     5            5           13m
$
$kubectl delete deployment employee-service-deployment
deployment.apps "employee-service-deployment" deleted
$
$kubectl get deployment
No resources found in default namespace.