# Run a Stateless Application Using a Deployment LLMS index: [llms.txt](/llms.txt) --- 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. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. 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:

    application/deployment.yaml
    
apiVersion: apps/v1
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: ```shell kubectl apply -f https://k8s.io/examples/application/deployment.yaml ``` 1. Display information about the Deployment: ```shell kubectl describe deployment nginx-deployment ``` The output is similar to this: ``` 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: Mounts: Volumes: Conditions: Type Status Reason ---- ------ ------ Available True MinimumReplicasAvailable Progressing True NewReplicaSetAvailable OldReplicaSets: NewReplicaSet: nginx-deployment-1771418926 (2/2 replicas created) No events. ``` 1. List the Pods created by the deployment: ```shell 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 ``` 1. Display information about a Pod: ```shell kubectl describe pod ``` where `` 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.

    application/deployment-update.yaml
    
apiVersion: apps/v1
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: ```shell kubectl apply -f https://k8s.io/examples/application/deployment-update.yaml ``` 1. Watch the deployment create pods with new names and delete the old pods: ```shell 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:

    application/deployment-scale.yaml
    
apiVersion: apps/v1
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:1.16.1
        ports:
        - containerPort: 80

1. Apply the new YAML file: ```shell kubectl apply -f https://k8s.io/examples/application/deployment-scale.yaml ``` 1. Verify that the Deployment has four Pods: ```shell 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 ``` For detailed scaling procedures including scaling down and scaling to zero, see [Scale a Deployment Manually](/docs/tasks/run-application/scale-deployment/). ## Deleting a deployment Delete the deployment by name: ```shell 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](/docs/concepts/workloads/controllers/replicationcontroller/). ## What's next - Learn more about [Deployment objects](/docs/concepts/workloads/controllers/deployment/). - Learn how to [update a Deployment without downtime](/docs/tasks/run-application/update-deployment-rolling/).