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Kubernetes quick tutorial
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
npm init -y
2. Install the dependencies
npm i express
3. Create a new file called index.js
touch index.js
Let's create a simple Express server that listens on port 3000 and returns a response.
//simple express serverconst 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:
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
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:
FROM node:19-alpine# Create app directoryWORKDIR /app# Copy package.json and package-lock.jsonCOPY package*.json ./# Install dependenciesRUN npm install# Copy source codeCOPY . .# Expose port 3000EXPOSE 3000# Run the appCMD [ "node", "index.js" ]
To build the app, let's populate the docker-compose.yml
file with the following:
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 fileservices:
- the services (containers) we want to run. In this case, just one.myapp:
- the name of the servicecontainer_name: myapp
- the name of the containerimage: myapp:1.0.0
- the name of the imagebuild: .
- 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!
//simple express serverconst 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:
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!
//simple express serverconst 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:
docker compose build
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:
apiVersion: apps/v1kind: Deploymentmetadata: name: myappspec: 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 APIkind: Deployment
- the kind of object we want to create. In this case, a deployment.name: myapp
- the name of the deploymentreplicas: 3
- the number of replicas of the deploymentimage: myapp:1.0
- the image of the container. We defined this in the docker-compose.yml fileports:
- 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:
kubectl get deployments
Let's create the deployment by typing:
kubectl apply -f deployment.yaml
Then let's try to get the deployments again:
kubectl get deployments
We can also get a detail of the pods:
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:
apiVersion: v1kind: Servicemetadata: name: myappspec: 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:
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:
kubectl apply -f service.yaml
Then let's try to get the services again:
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:
kubectl delete -f deployment.yamlkubectl 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): https://youtu.be/noJmOirhHKM
That's all.
If you have any questions, drop a comment below.
Original Link: https://dev.to/francescoxx/kubernetes-quick-tutorial-2el7
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