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Deployment - Declarative

  • In this lab we will create Kubernetes deployments using declarative YAML files.
  • We will deploy nginx, scale it up and down, and observe how Kubernetes manages replicas.

What will we learn?

  • How to create a deployment using a YAML file
  • How to apply changes using kubectl apply
  • How to scale replicas declaratively and imperatively
  • How Kubernetes handles scaling up and down

Prerequisites

  • A running Kubernetes cluster (kubectl cluster-info should work)
  • kubectl configured against the cluster

01. Create Namespace

  • As completed in the previous lab, create the desired namespace [codewizard]:
kubectl create namespace codewizard
namespace/codewizard created

02. Deploy nginx Using YAML File (Declarative)

  • Let’s create the YAML file for the deployment.
  • If this is your first k8s YAML file, its advisable that you type it in order to get the feeling of the structure.
  • Save the file with the following name: nginx.yaml
apiVersion: apps/v1
kind: Deployment # We use a deployment and not pod !!!!
metadata:
  name: nginx # Deployment name
  namespace: codewizard
  labels:
    app: nginx # Deployment label
spec:
  replicas: 2
  selector:
    matchLabels: # Labels for the replica selector
      app: nginx
  template:
    metadata:
      labels:
        app: nginx # Labels for the replica selector
        version: "1.17" # Specify specific verion if required
    spec:
      containers:
        - name: nginx # The name of the pod
          image: nginx:1.17 # The image which we will deploy
          ports:
            - containerPort: 80
  • Create the deployment using the -f flag & --record=true
kubectl apply -n codewizard -f nginx.yaml --record=true
deployment.extensions/nginx created

03. Verify That the Deployment Has Been Created

kubectl get deployments -n codewizard
NAME        DESIRED   CURRENT   UP-TO-DATE   AVAILABLE
multitool   1         1         1            1
nginx       1         1         1            1

04. Check if the Pods Are Running

kubectl get pods -n codewizard
NAME                         READY   STATUS    RESTARTS
multitool-7885b5f94f-9s7xh   1/1     Running   0
nginx-647fb5956d-v8d2w       1/1     Running   0

05. Playing with K8S Replicas

  • Let’s play with the replica and see K8S in action.
  • Open a second terminal and execute:
kubectl get pods -n codewizard --watch

06. Update the nginx.yaml File with Replica’s Value of 5

spec:
  replicas: 5

07. Update the Deployment Using kubectl apply

kubectl apply -n codewizard -f nginx.yaml --record=true
deployment.apps/nginx configured
  • Switch to the second terminal and you should see something like the following:
kubectl get pods --watch -n codewizard
NAME                         READY   STATUS    RESTARTS   AGE
multitool-74477484b8-dj7th   1/1     Running   0          20m
nginx-dc8bb9b45-hqdv9        1/1     Running   0          111s
nginx-dc8bb9b45-vdmp5        0/1     Pending   0          0s
nginx-dc8bb9b45-28wwq        0/1     Pending   0          0s
nginx-dc8bb9b45-wkc68        0/1     Pending   0          0s
nginx-dc8bb9b45-vdmp5        0/1     Pending   0          0s
nginx-dc8bb9b45-28wwq        0/1     Pending   0          0s
nginx-dc8bb9b45-x7j4g        0/1     Pending   0          0s
nginx-dc8bb9b45-wkc68        0/1     Pending   0          0s
nginx-dc8bb9b45-x7j4g        0/1     Pending   0          0s
nginx-dc8bb9b45-vdmp5        0/1     ContainerCreating   0          0s
nginx-dc8bb9b45-28wwq        0/1     ContainerCreating   0          0s
nginx-dc8bb9b45-wkc68        0/1     ContainerCreating   0          0s
nginx-dc8bb9b45-x7j4g        0/1     ContainerCreating   0          0s
nginx-dc8bb9b45-vdmp5        1/1     Running             0          2s
nginx-dc8bb9b45-28wwq        1/1     Running             0          3s
nginx-dc8bb9b45-x7j4g        1/1     Running             0          3s
nginx-dc8bb9b45-wkc68        1/1     Running             0          3s
  • Can you explain what do you see?

Why are there more containers than requested?

08. Scaling Down with kubectl scale

  • Scaling down using kubectl, and not by editing the YAML file:
kubectl scale -n codewizard --replicas=1 deployment/nginx
  • Switch to the second terminal. The current output should show something like this:
NAME                         READY   STATUS    RESTARTS   AGE
multitool-74477484b8-dj7th   1/1     Running   0          29m
nginx-dc8bb9b45-28wwq        1/1     Running   0          4m41s
nginx-dc8bb9b45-hqdv9        1/1     Running   0          10m
nginx-dc8bb9b45-vdmp5        1/1     Running   0          4m41s
nginx-dc8bb9b45-wkc68        1/1     Running   0          4m41s
nginx-dc8bb9b45-x7j4g        1/1     Running   0          4m41s
nginx-dc8bb9b45-x7j4g        1/1     Terminating   0          6m21s
nginx-dc8bb9b45-vdmp5        1/1     Terminating   0          6m21s
nginx-dc8bb9b45-28wwq        1/1     Terminating   0          6m21s
nginx-dc8bb9b45-wkc68        1/1     Terminating   0          6m21s
nginx-dc8bb9b45-x7j4g        0/1     Terminating   0          6m22s
nginx-dc8bb9b45-vdmp5        0/1     Terminating   0          6m22s
nginx-dc8bb9b45-wkc68        0/1     Terminating   0          6m22s
nginx-dc8bb9b45-28wwq        0/1     Terminating   0          6m22s
nginx-dc8bb9b45-28wwq        0/1     Terminating   0          6m26s
nginx-dc8bb9b45-28wwq        0/1     Terminating   0          6m26s
nginx-dc8bb9b45-vdmp5        0/1     Terminating   0          6m26s
nginx-dc8bb9b45-vdmp5        0/1     Terminating   0          6m26s
nginx-dc8bb9b45-wkc68        0/1     Terminating   0          6m27s
nginx-dc8bb9b45-wkc68        0/1     Terminating   0          6m27s
nginx-dc8bb9b45-x7j4g        0/1     Terminating   0          6m27s
nginx-dc8bb9b45-x7j4g        0/1     Terminating   0          6m27s

Cleanup

kubectl delete deployment nginx -n codewizard
kubectl delete deployment multitool -n codewizard