3. Kubernetes Cluster

Note

Make sure you have prepared the environment for this task.

Solution 3.1 - Create Kubernetes Cluster

Start Kubernetes Cluster

  1. Open Vagrant shell: vagrant ssh

  2. Get k3s: curl -sfL https://get.k3s.io | sh

  3. Check nodes: kubectl get no

Warning

To stop the Kubernetes cluster, run the command as the root user: shutdown -h now

Solution 3.2 - Deploy Application to the Kubernetes Cluster

  1. Run the app at a cluster: kubectl run POD_NAME --image=DOCKER_IMAGE_PATH

  2. Check the pod status using one of the following commands: kubectl get pods

  3. Deploy the app to the cluster directly from the Docker Hub: kubectl create deployment DEPLOYMENT_NAME --image=docker.io/DOCKERHUB_USERNAME/DOKER_IMAGE_NAME:TAG

  4. Access the application on localhost: kubectl port-forward POD_NAME 8080:8080

Kubeconfig

  • K3s stores the kubeconfig file under /etc/rancher/k3s/k3s.yaml

  • API server - https://127.0.0.1:8080

  • Authentication mechanism - username (admin) and password

Useful kubectl Commands

  • Get the control plane and add-ons endpoints: kubectl cluster-info

  • Get all the nodes in the cluster: kubectl get nodes

  • Get extra details about the nodes: kubectl get nodes -o wide

  • Get all the configuration details about the node: kubectl describe node NODE_NAME

  • Get basic pods information: kubectl get pods

  • Check the detailed information of a particular pod: kubectl describe pod POD_NAME

  • Delete pod: kubectl delete pod POD_NAME

Find out more in kubectl Cheat Sheet

Explore kubectl predefined assets in the video tutorial

Solution 3.3 - Define and Deploy Kubernetes Resources

  1. Create the namespace:

kubectl create ns demo

  1. Label the namespace:

kubectl label ns demo tier=test

  1. Create the nginx-alpine deployment:

kubectl create deploy nginx-alpine --image=nginx:alpine  --replicas=3 --namespace demo

  1. Label the deployment:

kubectl label deploy nginx-alpine app=nginx tag=alpine --namespace demo

  1. Expose the nginx-alpine deployment:

kubectl expose deployment nginx-alpine --port=8111 --namespace demo

  1. Create a config map:

kubectl create configmap nginx-version --from-literal=version=alpine --namespace demo

Common Errors & How to Fix Them

Permission Denied Error

The error message might look like this:

Error

Unable to read /etc/rancher/k3s/k3s.yaml, please start server with --write-kubeconfig-mode to modify kube config permissions error: error loading config file "/etc/rancher/k3s/k3s.yaml": open /etc/rancher/k3s/k3s.yaml: permission denied

To fix Permission Denied Error, run one of these commands:

  • sudo chmod 644 /etc/rancher/k3s/k3s.yaml: changing access in k3s.yaml

  • sudo su: setting the superuser permissions

Create Container Error

This type of error related to the status of the pod. The error message might look like this:

Error

Error: container create failed: time="2021-04-11T21:03:07Z" level=error msg="container_linux.go:366: starting container process caused: exec: \"cluster-kube-scheduler-operator\": executable file not found in $PATH"

To fix Create Container Error, use command: zypper install -t pattern apparmor