Deployments

• A Deployment named nginx-deployment is created, indicated by the .metadata.name field.

• The Deployment creates three replicated Pods, indicated by the .spec.replicas field.

• The .spec.selector field defines how the Deployment finds which Pods to manage. In this case, you select a label that is defined in the Pod template (app: nginx). However, more sophisticated selection rules are possible, as long as the Pod template itself satisfies the rule.

Before you begin, make sure your Kubernetes cluster is up and running. Follow the steps given below to create the above Deployment:

1. Create the Deployment by running the following command:

kubectl apply -f https://k8s.io/examples/controllers/nginx-deployment.yaml

1. Run kubectl get deployments to check if the Deployment was created.

kubectl get deployments

• When you inspect the Deployments in your cluster, the following fields are displayed:

  • NAME lists the names of the Deployments in the namespace.

  • READY displays how many replicas of the application are available to your users. It follows the pattern ready/desired.

  • UP-TO-DATE displays the number of replicas that have been updated to achieve the desired state.

  • AVAILABLE displays how many replicas of the application are available to your users.

  • AGE displays the amount of time that the application has been running.

  Notice how the number of desired replicas is 3 according to .spec.replicas field.

1. To see the Deployment rollout status, run `kubectl rollout status deployment/nginx-deployment`.

```bash
kubectl rollout status deployment/nginx-deployment
```



The output is similar to:

```
Waiting for rollout to finish: 2 out of 3 new replicas have been updated...
deployment "nginx-deployment" successfully rolled out
```



1. Run the `kubectl get deployments` again a few seconds later. 

kubectl get deployments

Notice that the Deployment has created all three replicas, and all replicas are up-to-date (they contain the latest Pod template) and available.

1. To see the ReplicaSet (rs) created by the Deployment, run kubectl get rs.

kubectl get rs

The output is similar to this:

```
NAME                          DESIRED   CURRENT   READY   AGE
nginx-deployment-75675f5897   3         3         3       18s
```

To see the labels automatically generated for each Pod.

kubectl get pods --show-labels

Assume that today we'd like to scale our nginx Pods from two to four:

kubectl scale --replicas=<expected_replica_num> deployment <deployment_name># kubectl scale --replicas=4 deployment my-nginx