Kubernetes YAML for a deployment

Below is the Kubernetes YAML file for creating a deployment. The deployment would control 3 replicas of nginx app.

~/kubernetes$ cat deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-nginx
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80

Explanation of each field in YAML

Below is the explanation of each of the lines in the YAML file.

kind: Deployment name: deployment-nginx	Create a deployment with the name “deployment-nginx“.
labels: app: nginx	The label for the deployment is “nginx“. Anytime we want to select this deployment among different deployments, we can use this label.
replicas: 3	Create 3 replicas of the deployment spec. Here, it includes the creation of pods with the name “nginx“; hence create 3 of them.
template: metadata: labels: app: nginx	The pods are labeled as nginx.
selector: matchLabels: app: nginx	The deployment would control pods that are labeled as “nginx“.

Running the YAML file

We have created a Kubernetes 2 node cluster with the client machine where we issue the kubectl command as below. We deploy the YAML file using “kubectl create” and check the pods, replicas, and deployment status using the below commands.

~/kubernetes$ kubectl create -f deployment.yaml
deployment.apps/deployment-nginx created

~/kubernetes$ kubectl get deployment
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
deployment-nginx   0/3     3            0           10s

~/kubernetes$ kubectl get deployment
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
deployment-nginx   3/3     3            3           17s

~/kubernetes$ kubectl get all
NAME                                   READY   STATUS    RESTARTS   AGE
pod/deployment-nginx-cd55c47f5-8lpgm   1/1     Running   0          25s
pod/deployment-nginx-cd55c47f5-zfwqk   1/1     Running   0          25s
pod/deployment-nginx-cd55c47f5-zxhjq   1/1     Running   0          25s

NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   10.245.0.1   <none>        443/TCP   8d

NAME                               READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/deployment-nginx   3/3     3            3           26s

NAME                                         DESIRED   CURRENT   READY   AGE
replicaset.apps/deployment-nginx-cd55c47f5   3         3         3       26s