k8s-intro

Useful beginners intro to Kubernetes

Note: To follow this tutorial you need to install minikube locally. Here the instructions: https://github.com/kubernetes/minikube/

Initial commands

minikube start

Start the cluster with start command, now have a running Kubernetes cluster in your terminal. Minikube just started a virtual machine, and a Kubernetes cluster is now running in that VM.

kubectl cluster-info

Kubernetes command line interface, kubectl, With Kubernetes we have a running master and a dashboard. The dashboard allows you to view your applications in a UI.

kubectl get nodes

This command shows all nodes that can be used to host our applications. Status Ready: this node it is ready to accept applications for deployment.

kubectl get deployments

List your deployments. In this case, there is 1 deployment running a single instance of kubernetes-bootcamp. (The instance is running inside a Docker container on that node).

Pods that are running inside Kubernetes are running on a private, isolated network. By default they are visible from other pods and services within the same kubernetes cluster, but not outside that network. When we use kubectl, we're interacting through an API endpoint to communicate with our application.

kubectl delete deployment <deploy-name>

Note that every pod is generated based on its deployment file. Hence, every time you delete a pod, it comes up again because you defined the value 'replicas: X' in the deployment file.

To delete a Pod/s permanently, You will have to first delete the deployment file of that pod and then delete the pod. This will delete the pod permanently. And of course, the deployment itself will be deleted permanently. The command to do that is

kubectl delete -f deployment_file_name.yml

And sure you can alternatively, delete the deployment file from Kubernetes's UI as well.

kubernetes Bootcamp sample app

kubectl run kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1 --port=8080

The run command creates a new deployment. Here we include the deployment name, app image location (include the full repository url for images hosted outside Docker hub), and specific port.

This command performed a few things for you:

• Searched for a suitable node where an instance of the application could be run (we have only 1 available node)
• Scheduled the application to run on that Node
• Configured the cluster to reschedule the instance on a new Node when needed

kubectl get deployments

Run this command to check your current deployment of kubernetes-bootcamp

Kubectl Proxy

kubectl proxy

This kubectl command create a proxy that will forward communications into the cluster-wide, private network. The proxy can be terminated by pressing control-C and won't show any output while its running.

With the proxy running now have a connection between our host and the Kubernetes cluster. The proxy enables direct access to the API from these terminals. Kubernetes hosted APIs now are available at: http://localhost:8001.

To get the version: http://localhost:8001/version

Pod API

The API server will automatically create an endpoint for each pod, based on the pod name, that is also accessible through the proxy. First we need to get the Pod name, and we'll store in the environment variable POD_NAME:

export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')

echo $POD_NAME

Now we can make an HTTP request to the application running in that pod: http://localhost:8001/api/v1/proxy/namespaces/default/pods/$POD_NAME/