Kubernetes Learning

• Hello world application in Kubernetes
• Build a custom docker image for PHP, nginx application & publish to the docker Hub
• Write a deployment script for PHP,Nginx & Mysql using the custom docker image build previously
• Install laravel application and configured to run inside kubernetes clusters
• Scale the Laravel application horizontally
• Write more advance scaling logic to scale application based on cpu use etc.
• Load Test
• Scale MySQL database using Vitess
• use redis as session storage and scale it

Pod, Service & Deployment

A Pod is the smallest deployable unit in Kubernetes. It represents a single instance of a running process in your cluster.

Service

A Service is an abstraction that defines a logical set of Pods and provides a stable endpoint to access them. It enables communication between Pods or external clients and Pods.

Key Characteristics:

• Stable Networking: Provides a consistent IP address and DNS name, even as Pods are replaced or scaled.
• Load Balancing: Distributes traffic across multiple Pods matching its selector.
  • Service Types:
    • ClusterIP (default): Internal communication within the cluster.
    • NodePort: Exposes the service on a port of each node for external access.
    • LoadBalancer: Exposes the service externally using a cloud provider's load balancer.
    • ExternalName: Maps the service to an external DNS name

Deployment

A Deployment is a controller that manages Pods and ensures they are running in the desired state. It allows you to define and manage the number of replicas (instances), updates, and rollbacks for your application.

Install kubectl

The Kubernetes command-line tool, kubectl, allows you to run commands against Kubernetes clusters. You can use kubectl to deploy applications, inspect and manage cluster resources, and view logs. Link

Hello World in Kubernetes

We can start create a very first deployment using a public docker image.

kubectl create deployment nginx-deployment --image=nginx

The above deployment can be exposed outside the container & kubernetes using expose command.

kubectl expose deployment nginx-deploment --type=LoadBalancer --port=8080 --target-port=80

The above command creates a service for the 'nginx-deployment' deployment with a LoadBalancer type, enabling access to our Kubernetes cluster from outside the container.

You can use following commands to get details about pods:

Commands	Descriptions
kubectl get pods	Get all the pods
kubectl get pods -o wide	get all pods with IP addresses
kubectl describe pod nignx-65cfcbff97-b8ccx	Get the details of a pod

You can use following commands to get details about deployments:

Commands	Descriptions
kubectl get deployments	Get all the deployments
kubectl delete deployments --all	delete all the deployments

Services

Commands	Descriptions
kubectl get services	Get all the services
kubectl describe service nginx-deployment	Detail of a service

The kubectl get services returns the following:

kubectl get services
NAME                TYPE           CLUSTER-IP        EXTERNAL-IP    PORT(S)          AGE
php                 ClusterIP      192.168.194.147   <none>         9000/TCP         35h
kubernetes          ClusterIP      192.168.194.129   <none>         443/TCP          35h
nginx               NodePort       192.168.194.181   <none>         8080:32539/TCP   35h
nginx-deploment-1   LoadBalancer   192.168.194.248   198.19.249.2   8081:32479/TCP   34h
mysql               NodePort       192.168.194.218   <none>         4406:32740/TCP   105m

• nginx-deployment-1 Service: External IP: 198.19.249.2 (assigned via LoadBalancer) and Exposed Port (NodePort): 32479, so it can be accessed from http://198.19.249.2:32539

• NodePort Service (nginx): For NodePort services, the application is accessible via: http://<node-ip>:32539 Here, refers to the IP of the node running the cluster. If it's running on orbstack: kubectl get nodes -o wide to get <node-ip>.

Load-balancer

Minikube Dashboard

Commands	Descriptions
minikube start
`minikube dashboard	Start the minikube dashboard

Exposing Application

If your service type is ClusterIP (default), it’s only accessible within the cluster. Access via kubectl port-forward: Forward the service port to your local machine:

kubectl port-forward svc/nginx 8080:80

To check if nginx is working

kubectl logs <nginx-pod-name>

Scaling

Scaling a deployment by running the following commands:

kubectl scale deployment <nginx-deployment> --replicas=1

Applying changes

kubectl apply -f k8s/nginx-service.yaml

Managing .ENV

Kubernetes allows to create a secret based on .env file, and these secret can be referenced to create a deployment scripts.

kubectl create secret generic env-secret --from-env-file=./application/.env --dry-run=client -o yaml > k8s/env-secret.yaml

Debugging

You can use the following command to view the details of all Pods, or specify a Pod name to inspect a particular Pod.

Commands	Descriptions
kubectl describe pod
kubectl describe pod <podname> -n <namespace>	Start the minikube dashboard

SSH Connection

A pod can be accessed with SSH Connection as:

Commands	Descriptions
kubectl exec -it <POD> -- <COMMAND>

Example of database connection from PHP cluster:

<?php
$servername = "mysql";
$username   = "root";
$password   = "12345678";
$database   = "jh";
$port       = 4406;

$conn = new mysqli($servername, $username, $password, $database, $port);

if ($conn->connect_error) {
    die("Connection failed: ".$conn->connect_error);
}
echo "Connected successfully!";

Deploying custom docker Image with k8:

Since k8 can't use local docker image, so we need to push it to the container registry. To build php image

docker build -t 9813276057/application-php:v0.0.1 ./php/

To build the nginx Image

docker build -t 9813276057/application-nginx ./nginx/

After building the images, push it to the container hub:

docker push 9813276057/application-php:v0.0.1

docker push 9813276057/application-nginx