At the beginning, take a look at the Deployment you just created and its ReplicaSet by executing the following code block:

$ kubectl describe deployment simple-nginx
Name:                   simple-nginx
Namespace:              default
CreationTimestamp:      Fri, 04 May 2018 12:14:21 -0400
Labels:                 env=test
                        project=My-Happy-Web
                        role=frontend
Annotations:            deployment.kubernetes.io/revision=1
Selector:               env=test,project=My-Happy-Web,role=frontend
Replicas:               5 desired | 5 updated | 5 total | 5 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  1 max unavailable, 1 max surge
Pod Template:
  Labels:  env=test
           project=My-Happy-Web
           role=frontend
  Containers:
   simple-nginx:
    Image:        nginx
    Port:         80/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      True    MinimumReplicasAvailable
  Progressing    True    NewReplicaSetAvailable
OldReplicaSets:  <none>
NewReplicaSet:   simple-nginx-585f6cddcd (5/5 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  1h    deployment-controller  Scaled up replica set simple-nginx-585f6cddcd to 5
// rs is the abbreviated resource key of replicaset
$ kubectl get rs
NAME                      DESIRED   CURRENT   READY     AGE
simple-nginx-585f6cddcd   5         5         5         1h

Based on the preceding output, we know that the default updating strategy of deployment is rolling-update. Also, there is a single ReplicaSet named <Deployment Name>-<hex decimal hash> that is created along with the Deployment.

Next, check the content of the current Service endpoint for the sake of verifying our update later:

// record the cluster IP of Service "nginx-service"
$ export SERVICE_URL=$(kubectl get svc | grep nginx-service | awk '{print $3}'):8080

// For minikube environment only, record the VM host IP and port for the service
$ export SERVICE_URL=$(minikube service nginx-service --url)
$ curl $SERVICE_URL | grep "title"
<title>Welcome to nginx!</title>

We will get the welcome message in the title of the HTML response with the original nginx image.