👋 Introduction

Let's make the simplest but understandable Kubernetes example ever.

Video version:

We will create our first example with Kubernetes starting from scratch, using: JavaScript Node.js Docker Docker Compose Kubernetes ## 📃 Requirements Node.js Docker (with Kubernetes enabled) --- ## 🚀 Getting started Let's start in a new VS Code window (or any other editor of your choice). ### 1. Create a new project bash npm init -y ### 2. Install the dependencies bash npm i express ### 3. Create a new file called index.js js touch index.js Let's create a simple Express server that listens on port 3000 and returns a response. js //simple express server const express = require('express'); const app = express(); app.get('/', (req, res) => { res.send('Hello World!'); }); app.listen(3000, () => { console.log('Example app listening on port 3000!'); }); Run this by typing: plaintext node index.js Now it's time to Dockerize our application. --- ## 🐳 Dockerizing our application We will dockerize the application by creating three files: .dockignore Dockerfile docker-compose.yml plaintext touch .dockignore Dockerfile docker-compose.yml ### ❌ .dockignore Add node_modules to the file This is to ignore the local node_modules folder when building the image. ### 🐳 Dockerfile Open the Dockerfile and add the following: plaintext FROM node:19-alpine # Create app directory WORKDIR /app # Copy package.json and package-lock.json COPY package*.json ./ # Install dependencies RUN npm install # Copy source code COPY . . # Expose port 3000 EXPOSE 3000 # Run the app CMD [ "node", "index.js" ] To build the app, let's populate the docker-compose.yml file with the following: yaml version: '3.9' services: myapp: container_name: myapp image: myapp:1.0.0 build: . ports: - 3000:3000 Explanation of the docker-compose.yml file: version: '3.9' - the version of the docker-compose file services: - the services (containers) we want to run. In this case, just one. myapp: - the name of the service container_name: myapp - the name of the container image: myapp:1.0.0 - the name of the image build: . - the path to the Dockerfile. In this case, the current directory. ports: - the ports that we want to expose. In this case, port 3000 of the container will be exposed on port 3000 of the host machine. Before we test it with Docker, let's modify the index.js file by changing Hello World! to Hello Docker! js //simple express server const express = require('express'); const app = express(); app.get('/', (req, res) => { res.send('Hello Docker!'); }); app.listen(3000, () => { console.log('Example app listening on port 3000!'); }); Now let's run the container by typing this in the terminal: bash docker compose up Nice! Now it's the turn of Kubernetes. But before we do that, let's change the Hello Docker! to Hello Kubernetes! js //simple express server const express = require('express'); const app = express(); app.get('/', (req, res) => { res.send('Hello Kubernetes!'); }); app.listen(3000, () => { console.log('Example app listening on port 3000!'); }); Then rebuild the image by typing: plaintext docker compose build ℹ️ This is not really necessary, but good to understand how it works. --- ## ☸️ Kubernetes Before we start, be sure Kubernetes is enabled in Docker Desktop. ### Pods, Deployments, and Services Kubernetes is a container orchestration tool. It is used to manage multiple containers on multiple hosts. In our case, we will use our machine as a single host. We will keep it as minimal as possible by creating a deployment and a service. Just three definitions to get started as soon as possible. pod: the smallest deployable unit of computing that can be created and managed in Kubernetes. deployment: a Kubernetes object that manages a set of pods. It is responsible for creating and updating pods. service: an abstraction that defines a logical set of pods and a policy by which to access them. They are used to expose a set of pods to external traffic. ### 📝 Create the deployment We will create a deployment in less than 20 lines of code. At the root of the project, create a new file called deployment.yaml and add the following: yaml apiVersion: apps/v1 kind: Deployment metadata: name: myapp spec: replicas: 3 selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp image: myapp:1.0 ports: - containerPort: 3000 ⚠️ You might see a warning in the last five lines, but it's only because this configuration might eat a lot of resources. But let's keep it simple for now. Explanation of the deployment.yaml file: apiVersion: apps/v1 - the version of the Kubernetes API kind: Deployment - the kind of object we want to create. In this case, a deployment. name: myapp - the name of the deployment replicas: 3 - the number of replicas of the deployment image: myapp:1.0 - the image of the container. We defined this in the docker-compose.yml file ports: - the ports of the container. 3000 in this case. Before we create the deployment, let's check if there are any deployments in the cluster: bash kubectl get deployments Let's create the deployment by typing: bash kubectl apply -f deployment.yaml Then let's try to get the deployments again: bash kubectl get deployments We can also get a detail of the pods: bash kubectl get pods As you can see, we have 3/3 pods running (we defined replicas: 3 in the deployment.yaml file). But creating a deployment is not enough. We need to expose the deployment to the outside world! ### 🌐 Create the service We will create a service in 11 lines of code. At the root of the project, create a new file called service.yaml and add the following: yaml apiVersion: v1 kind: Service metadata: name: myapp spec: selector: app: myapp ports: - port: 80 targetPort: 3000 type: LoadBalancer This is enough to expose the deployment to the outside world (port 80) Before we apply this configuration, let's check if there are any services in the cluster: bash kubectl get services There is one called Kubernetes but that's the default service that is created when you install Kubernetes. Let's create the service by typing: bash kubectl apply -f service.yaml Then let's try to get the services again: bash kubectl get services Finally, visit localhost:80 in your browser and you should see Hello Kubernetes! ### 🧹 Clean up To clean up, delete the deployment and the service: bash kubectl delete -f deployment.yaml kubectl delete -f service.yaml ### 🏁 Conclusion We did it! We created our first example with Kubernetes starting from scratch, using: JavaScript Node.js Docker Docker Compose Kubernetes Video Version:

All the code is available in the GitHub repository (link in the video description): youtu.be/noJmOirhHKM

That's all.

If you have any questions, drop a comment below.

Francesco