View source for 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