Run a Stateless Application Using a Deployment

This page shows how to run an application using a Kubernetes Deployment object.

Objectives

  • Create an nginx deployment.
  • Use kubectl to list information about the deployment.
  • Update the deployment.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

Your Kubernetes server must be at or later than version v1.9. To check the version, enter kubectl version.

Creating and exploring an nginx deployment

You can run an application by creating a Kubernetes Deployment object, and you can describe a Deployment in a YAML file. For example, this YAML file describes a Deployment that runs the nginx:1.14.2 Docker image:

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2 # tells deployment to run 2 pods matching the template
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80
  1. Create a Deployment based on the YAML file:

     kubectl apply -f https://k8s.io/examples/application/deployment.yaml
    
  2. Display information about the Deployment:

     kubectl describe deployment nginx-deployment
    

    The output is similar to this:

     user@computer:~/website$ kubectl describe deployment nginx-deployment
     Name:     nginx-deployment
     Namespace:    default
     CreationTimestamp:  Tue, 30 Aug 2016 18:11:37 -0700
     Labels:     app=nginx
     Annotations:    deployment.kubernetes.io/revision=1
     Selector:   app=nginx
     Replicas:   2 desired | 2 updated | 2 total | 2 available | 0 unavailable
     StrategyType:   RollingUpdate
     MinReadySeconds:  0
     RollingUpdateStrategy:  1 max unavailable, 1 max surge
     Pod Template:
       Labels:       app=nginx
       Containers:
        nginx:
         Image:              nginx:1.14.2
         Port:               80/TCP
         Environment:        <none>
         Mounts:             <none>
       Volumes:              <none>
     Conditions:
       Type          Status  Reason
       ----          ------  ------
       Available     True    MinimumReplicasAvailable
       Progressing   True    NewReplicaSetAvailable
     OldReplicaSets:   <none>
     NewReplicaSet:    nginx-deployment-1771418926 (2/2 replicas created)
     No events.
    
  3. List the Pods created by the deployment:

     kubectl get pods -l app=nginx
    

    The output is similar to this:

     NAME                                READY     STATUS    RESTARTS   AGE
     nginx-deployment-1771418926-7o5ns   1/1       Running   0          16h
     nginx-deployment-1771418926-r18az   1/1       Running   0          16h
    
  4. Display information about a Pod:

     kubectl describe pod <pod-name>
    

    where <pod-name> is the name of one of your Pods.

Updating the deployment

You can update the deployment by applying a new YAML file. This YAML file specifies that the deployment should be updated to use nginx 1.16.1.

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.16.1 # Update the version of nginx from 1.14.2 to 1.16.1
        ports:
        - containerPort: 80
  1. Apply the new YAML file:

      kubectl apply -f https://k8s.io/examples/application/deployment-update.yaml
    
  2. Watch the deployment create pods with new names and delete the old pods:

      kubectl get pods -l app=nginx
    

Scaling the application by increasing the replica count

You can increase the number of Pods in your Deployment by applying a new YAML file. This YAML file sets replicas to 4, which specifies that the Deployment should have four Pods:

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 4 # Update the replicas from 2 to 4
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80
  1. Apply the new YAML file:

     kubectl apply -f https://k8s.io/examples/application/deployment-scale.yaml
    
  2. Verify that the Deployment has four Pods:

     kubectl get pods -l app=nginx
    

    The output is similar to this:

     NAME                               READY     STATUS    RESTARTS   AGE
     nginx-deployment-148880595-4zdqq   1/1       Running   0          25s
     nginx-deployment-148880595-6zgi1   1/1       Running   0          25s
     nginx-deployment-148880595-fxcez   1/1       Running   0          2m
     nginx-deployment-148880595-rwovn   1/1       Running   0          2m
    

Deleting a deployment

Delete the deployment by name:

kubectl delete deployment nginx-deployment

ReplicationControllers -- the Old Way

The preferred way to create a replicated application is to use a Deployment, which in turn uses a ReplicaSet. Before the Deployment and ReplicaSet were added to Kubernetes, replicated applications were configured using a ReplicationController.

What's next

Last modified September 15, 2020 at 2:59 PM PST: Update run-stateless-application-deployment.md (42f23e75b)