Run a Stateless Application Using a Deployment
This page shows how to run an application using a Kubernetes Deployment object.
- Objectives
- Before you begin
- Creating and exploring an nginx deployment
- Updating the deployment
- Scaling the application by increasing the replica count
- Deleting a deployment
- ReplicationControllers – the Old Way
- What's next
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:
application/deployment.yaml
|
---|
|
Create a Deployment based on the YAML file:
kubectl apply -f https://k8s.io/examples/application/deployment.yaml
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.
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
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 1.8.
application/deployment-update.yaml
|
---|
|
Apply the new YAML file:
kubectl apply -f https://k8s.io/examples/application/deployment-update.yaml
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:
application/deployment-scale.yaml
|
---|
|
Apply the new YAML file:
kubectl apply -f https://k8s.io/examples/application/deployment-scale.yaml
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
- Learn more about Deployment objects.
Feedback
Was this page helpful?
Thanks for the feedback. If you have a specific, answerable question about how to use Kubernetes, ask it on Stack Overflow. Open an issue in the GitHub repo if you want to report a problem or suggest an improvement.