Kubernetes is a container orchestrator which helps to manage and scale application running on containers.
Setting up a production grade Kubernetes cluster is a hassle when it comes to provision different kind of nodes which manages a Kubernetes workload. In a Kubernetes cluster, there are two kinds of nodes

• Master Nodes (control plane) : These nodes manage and control how the application are "orchestrated". This simply means master nodes keeps track of current application state, does the current state of the deployment matches the desired state and so on. To sum it up, this is the brain of the Kubernetes cluster.

  • Worker Nodes: These are the actual nodes where the containers are provisioned and run. These are the nodes that actually handle the workload.

Note: There are other components to a Kubernetes cluster like Controller Manager, etcd etc. but that is beyond the scope of this post

For starters, knowing the above information is just right to get started with some hands-on on Kubernetes. While we can set up our own VM's as control nodes and worker nodes, but it is too much hassle to install all the components required to run a Kubernetes cluster.

Therefore, we will take use Minikube that comes with all the bells and whistles that are required to run a Kubernetes cluster with just few commands. Let us get started with some hands-on now. Fire up that terminal of your choice and start following

Assumption: You must have docker-desktop installed on your machine to follow along. Check if docker is installed on your system by running the following command in your terminal

docker -v

If you see something like this, then you are good to go 😄

~ ➜ docker -v
Docker version 20.10.12, build e91ed57

Installing Minikube

For macOS,

brew install minikube

For Windows,

choco install minikube

For Linux,

curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64
sudo install minikube-linux-amd64 /usr/local/bin/minikube

If you do not have brew installed on macOS or chocolatey installed on Windows, you can alternatively run:

For macOS,

curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube-darwin-amd64
sudo install minikube-darwin-amd64 /usr/local/bin/minikube

For Windows,
Follow instructions on Minikube for Windows

Start Minikube cluster

On your terminal, run the following command,

minikube start --vm-driver=docker

You should now see Minikube spinning up Kubernetes cluster for you. If you get output something like this, then you are good to go.

~ ➜ minikube start --vm-driver=docker
😄  minikube v1.25.2 on Darwin 12.3.1
🆕  Kubernetes 1.23.3 is now available. If you would like to upgrade, specify: --kubernetes-version=v1.23.3
✨  Using the docker driver based on existing profile
👍  Starting control plane node minikube in cluster minikube
🚜  Pulling base image ...
🐳  Preparing Kubernetes v1.23.1 on Docker 20.10.12 ...
    ▪ kubelet.housekeeping-interval=5m
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🌟  Enabled addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

You can now view the nodes created by Minikube by running kubectl get nodes command

~ ➜ kubectl get nodes                                                                                                                                                                                                
NAME       STATUS   ROLES                  AGE   VERSION
minikube   Ready    control-plane,master   23d   v1.23.1

As you can see, you now have a single node Minikube cluster running on your local machine. In the output you can see something interesting. There is only one node, which is the master node.

Now, you might be wondering where is the worker node that I told you at the beginning of this post. Well, Minikube creates a single node cluster by default, meaning that a single node act as both master and worker node.

This setup is fine since we are using this for our local development purpose. In actual production grade setup, the setup has multiple master and multiple worker node for high availability and to make the system fault-tolerant.

Note: Minikube also supports multi-node setup but that is a discussion meant for some other post. We will just work with single node cluster for this tutorial.

Now that we have the setup ready, we can now run our applications on this setup.
For the purpose of this tutorial we will use an echo-server by Google Cloud which when sent an HTTP request will echo out details about the HTTP request and client who sent that request.

Key Concepts

Before getting into the deployment, let us understand three basics concepts when it comes to Kubernetes.

• Pods: The smallest compute unit in a Kubernetes setup. The pods are the place where containers run (where the application code runs). Although a pod can run multiple containers, usually we see pods running one or two containers. For horizontal scaling, Kubernetes spawns multiple pods in a node so that the underlying application can scale.
• Deployment: This is a way we define a pod configuration. A pod configuration consists of what image to run, the number of replicas a pod can have, resource configuration etc. In short, a deployment is a way to run pods running containers at scale.
• Service: A service helps us to expose the underlying ports in the containers that we want to send network requests to. So services are tied to pods, making it a means to communicate with our application. No matter how many pods are running in the background we cannot connect to the service and in turn the Kubernetes service can help us communicate with the application. Kubernetes' service also act as a load balancer for the pods.

Now that we have enough background, let us deploy our first pod in the Kubernetes cluster on Minikube.

Your First Deployment

Run the following command in your terminal

kubectl create deployment hello-minikube --image=k8s.gcr.io/echoserver:1.4

So we have now created a deployment with a bare minimum specification which is a name for the deployment, and we have specified the container image to run.
Here hello-minikube is the name of the deployment and the image is specified using --image argument.

Now, let us verify if the pod is actually running. To see the pods running, run the following command kubectl get pods

~ ➜ kubectl get pods                                                                                                                                                                                                 
NAME                              READY   STATUS    RESTARTS   AGE
hello-minikube-7bc9d7884c-cb2fs   1/1     Running   0          78m

The pods are in RUNNING status and 1 replica is running. The 1/1 means that we have 1 replica running, currently out of 1 desired replica.

Exposing through a Service

Now that our echo server is running, How can we access the server ? If you now try to access localhost:8080 you will see Unable to connect error.

As I already mentioned, to access/communicate with pods, we need to expose the pods with a service. Let us create a service and expose port 8080 of the hello-minikube deployment. To create a service, run the following command

kubectl expose deployment hello-minikube --type=NodePort --port=8080

This command tells Kubernetes to expose the port 8080 of the pods of hello-minikube deployment. The service of type NodePort. Kubernetes has different types of services namely NodePort, ClusterIP, LoadBalancer etc.
We will dive deeper into the types of services in some other post, but for now let us just assume that using NodePort we can direct external traffic (HTTP request from host machine) to the Kubernetes cluster.

Now let us run kubectl get service command to see the details of the service that is created

~ ➜ kubectl get service                                                                                                                                                                                              
NAME             TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
hello-minikube   NodePort    10.103.34.250   <none>        8080:32262/TCP   78m
kubernetes       ClusterIP   10.96.0.1       <none>        443/TCP          21d

From the output, we see that a NodePort service named hello-minikube is created. So now let us hit localhost:8080. Uhhh Oh! We still cannot reach the echo-server.

Port Forwarding

There is one missing piece of the puzzle still left so that we can access the echo-server. So let us understand why is this not working even after exposing the deployment using the hello-minikube service?
The Minikube setup basically runs a VM where the application pods are running. We are trying to access the port that is exposed on the Minikube VM from our host machine. That is the reason the communication is not happening. Basically, the network does not know how to route traffic from host machine to Minikube VM.

To enable the routing of traffic from host machine, run kubectl port-forward service/hello-minikube 8080:8080

~ ➜ kubectl port-forward service/hello-minikube 8080:8080                                                                                                                                                            
Forwarding from 127.0.0.1:8080 -> 8080
Forwarding from [::1]:8080 -> 8080

Now, let us try to access our echo-server localhost:8080. Viola!! We are able to access our echo-server and it give us the see the following output. Here we can see the details of our request sent to the echo-server.

CLIENT VALUES:
client_address=127.0.0.1
command=GET
real path=/
query=nil
request_version=1.1
request_uri=http://localhost:8080/

SERVER VALUES:
server_version=nginx: 1.10.0 - lua: 10001

HEADERS RECEIVED:
accept=text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
accept-encoding=gzip, deflate, br
accept-language=en-US,en;q=0.5
connection=keep-alive
host=localhost:8080
sec-fetch-dest=document
sec-fetch-mode=navigate
sec-fetch-site=none
sec-fetch-user=?1
upgrade-insecure-requests=1
user-agent=Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:100.0) Gecko/20100101 Firefox/100.0
BODY:
-no body in request-

This command kubectl port-forward service/hello-minikube 8080:8080 allow us to port forward our request from our host machine at port 8080 to the pods port 8080.

Conclusion

So to wrap up we have successfully

• Set up a Kubernetes cluster
• Run pods and deployment
• Expose deployment using Kubernetes service
• Port-forwarded traffic from host machine to the Minikube VM

I hope now you are a little more comfortable in starting your own journey in Kubernetes. Feel free to share your journey with me!!

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