Project 6: Setting up communication between different Kubernetes deployments

For this project, I provisioned a Kubernetes cluster in my VM using minikube

Requirements :

• VirtualBox
• Minikube
• Kubectl

Create a Minikube node using the virtualBox driver

$ minikube  start --vm-driver=virtualbox

You could ssh into the node using ssh docker@$(minikube ip)

Take note the default minikube credentials are:

• username: docker
• password: tcuser

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The Plan

Step 1: Creating the Docker image

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First copy the ./k8s-web-to-nginx folder and paste in your working directory

• The index.mjs file contains a simple web server and 2 endpoints. The "/" enpoint responds with a greeting from the pod, and the "/nginx" endpoint displays the nginx homepage \
• The Dockerfile contains instructions needed to build the Docker image for our small application

Next, cd into the ./k8s-web-to-nginx folder and run the following command to build the docker image.

 $ docker build . -t 4568910/k8s-web-to-nginx

The -t flag allows us specify a tag name for this image. I used my dockerhub repo in the format {username}/{repo_name}

Next, goto hub.docker.com) and create a repo for our image k8s-web-to-nginx

The next step will be to push the image to your docker repo using:

$ docker push {docker_username}/k8s-web-to-nginx

In my case, that would be:

$ docker push 4568910/k8s-web-hello

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Step 2: Creating Deployments & Services

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In order to create the deployment and services, we will make use of the yaml file found at ./k8s-web-to-nginx.yaml

In this K8s manifest, the service part contains...

apiVersion: v1
kind: Service
metadata:
  name: k8s-web-to-nginx
spec:
  type: LoadBalancer
  selector: 
    app: k8s-web-to-nginx
  ports:
  - port: 3333
    targetPort: 3000

In this service part of the manifest:

• metadata contains the "name" of this service k8s-web-to-nginx
• spec describes the pod in more details
• • type is LoadBalancer
• • selector states keys and values that are to be matched by pods which intend to receive traffic from this service
• • port states a host port to map to the targetPort (ports from the Express server container)

And the Deployment part contains:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: k8s-web-to-nginx
spec:
  replicas: 4
  selector:
    matchLabels:
      app: k8s-web-to-nginx
  template:
    metadata:
      labels:
        app: k8s-web-to-nginx
    spec:
      containers:
      - name: k8s-web-to-nginx
        image: 4568910/k8s-web-to-nginx
        resources:
          limits:
            memory: "128Mi"
            cpu: "250m"
        ports:
        - containerPort: 3000

In the deployment manifest:

• metadata holds the name of htis deployment
• spec gives more details about the deployment
• • replicas is the number of desired pods
• • selector is a label selector for pods. Existing ReplicaSets whose pods are selected by this will be the ones affected by this deployment. It must match the pod template's labels.
• • template describes the pods that will be created.
• • • metadata can be used to organize and categorize (scope and select) objects. May match selectors of replication controllers (deployments) and services.
• • • spec Specification of the desired behavior of the pod.
• • • • containers describes resources for a list of containers belonging to the pod

The manifests for nginx are similar (but the service type is Cluster IP). Find and download it from nginx.yaml

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Step 3: Apply the yaml files to the cluster to begin initiate the creation of the resources

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To apply the manifests, run:

$ kubectl apply -f k8s-web-to-nginx.yaml -f nginx.yaml

And, hurray!!! Our setup is complete

In order to view our resources, run:

# to see our pods
$ kubectl get pods

# to see our service
$ kubectl get svc

# to see our deployments
$ kubectl get deploy

To visit the pages being served by our web server, if you're using minikube, run:

$ minikube service k8s-web-to-nginx

It will open a page in your web browser with a greeting from our pod (showing that our "/" endpoint was hit).

To go to our nginx endpoint, simply add "/nginx" in front of the address on the browser page. You should be redirected to the Nginx home page.

If this is what you get, it means everything works fine.

Here's a diagram showing the communication between both deployments:

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Step 4: Cleaning Up

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To remove deployments and services, run:

$ kubectl delete -f k8s-web-to-nginx.yaml -f nginx.yaml

And to stop minikube node, run:

$ minikube stop