Kubernetes simple deployment with service and configmap

Intro

This article is based on the previois installation: Install Kubernetes 1.26 on Debian 11 with Flannel, the aim is to setup:

• Simple cluster of two or more nginx pods
• Create a service on top
• Use the Configmap to create content
• Apply the new content

Deployment

deployment of 2 Nginx Pods (Replicas = 2)

• nginx-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend-deployment
  labels:
    app: web
    tier: frontend
spec:
  replicas: 2
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        app: web
        tier: frontend
    spec:
      containers:
      - image: nginx:latest
        name: nginx
        ports:
        - containerPort: 30080
          name: nginx

• Apply

kubectl apply -f nginx-deplyoment.yaml

• List

kubectl get pods -o wide
NAME                                   READY   STATUS    RESTARTS   AGE   IP            NODE             NOMINATED NODE   READINESS GATES
frontend-deployment-6fb5bf7f54-4l2nv   1/1     Running   0          36s   10.244.2.12   vm-c1-worker-2   <none>           <none>
frontend-deployment-6fb5bf7f54-mmfqb   1/1     Running   0          36s   10.244.1.10   vm-c1-worker-1   <none>           <none>

Service

The service maps the label/app to web and associate the container port to port 80

• service.yaml

apiVersion: v1
kind: Service
metadata:
  name: example-service
  labels:
    app: web
spec:
  type: NodePort
  selector:
    app: web
  ports:
    - protocol: TCP
      targetPort: 80
      port: 80
      nodePort: 30080

• Apply

kubectl apply -f service.yaml

• List

kubectl get service -o wide
NAME              TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE     SELECTOR
example-service   NodePort    10.111.177.255   <none>        80:30080/TCP   8s      app=web

Testing

• Apply commands to the Pod, we want to add the hostname to the nginx welcome page

kubectl get pods -o wide
NAME                                   READY   STATUS    RESTARTS   AGE   IP            NODE             NOMINATED NODE   READINESS GATES
frontend-deployment-6fb5bf7f54-nq2bl   1/1     Running   0          36s   10.244.2.12   vm-c1-worker-2   <none>           <none>
frontend-deployment-6fb5bf7f54-zj44m   1/1     Running   0          36s   10.244.1.10   vm-c1-worker-1   <none>           <none>

Run commands inside of the pod

• Get the hostname

kubectl exec frontend-deployment-6fb5bf7f54-nq2bl -- hostname

• Replace the message on the first Pod:

export khost=frontend-deployment-6fb5bf7f54-nq2bl
kubectl exec $khost -- \
sed -ir  "s/Welcome to nginx/Welcome to nginx on $HOSTNAME/gi" /usr/share/nginx/html/index.html

• Replace the message on the second Pod:

export khost=frontend-deployment-6fb5bf7f54-zj44m
kubectl exec $khost -- \
sed -ir  "s/Welcome to nginx/Welcome to nginx on $HOSTNAME/gi" /usr/share/nginx/html/index.html

• Use curl to alternate between the pods

curl -v --silent 10.111.177.255 2>&1 | grep '<title>'

Get own content into the Nginx Pods

Configmap

Get content to the cluster, create a simple index.html and add it to a configmap

kubectl create configmap index.html --from-file index.html

kubectl get configmaps
NAME               DATA   AGE
index.html         1      5m23s

kubectl describe configmap index.html
Name:         index.html
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
index.html:
...
...

Rewrite the deployment

• Add the volumes to nginx-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend-deployment
  labels:
    app: web
    tier: frontend
spec:
  replicas: 2
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        app: web
        tier: frontend
    spec:
      containers:
      - image: nginx:latest
        name: nginx
        ports:
        - containerPort: 30080
          name: nginx
        volumeMounts:
        - name: htmlcontent
          mountPath: "/usr/share/nginx/html/"
          readOnly: true
      volumes:
      - name: htmlcontent
        configMap:
          name: index.html
          items:
          - key: index.html
            path: index.html

kubectl apply -f nginx-deplyoment.yaml