chore: chapter 12

Author: lmammino

12-scalability-and-architectural-patterns/08-scaling-an-app-on-kubernetes/Dockerfile

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+FROM node:24-slim
+EXPOSE 8080
+COPY app.js package.json /app/
+WORKDIR /app
+CMD ["npm", "start"]

12-scalability-and-architectural-patterns/08-scaling-an-app-on-kubernetes/README.md

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+# 08-scaling-an-app-on-kubernetes
+
+This examples demonstrates how to deploy and scale a simple Node.js webserver on Kubernetes (using minikube)
+
+## Requirements
+
+Install [docker](https://docs.docker.com/get-docker/) and [minikube](https://kubernetes.io/docs/tasks/tools/install-minikube/)
+
+
+Once minikube is initialized (`minikube start`), on mac and linux, make sure to run `eval $(minikube docker-env)` to connect the docker daemon to the minikube virtual machine.
+
+## Run
+
+### 1. Build the image
+
+Build the docker image with:
+
+```bash
+docker build -t hello-web:v1 .
+```
+
+### 2. Add the app to the kubernetes cluster
+
+Start the minikube kubernetes dashboard to see how you local cluster changes with the various interactions we are going to perform:
+
+```bash
+minikube dashboard
+```
+
+Now, add the app to the kubernetes cluster with:
+
+```bash
+kubectl create deployment hello-web --image=hello-web:v1
+```
+
+To be able to access the application from your laptop you need to expose it:
+
+```bash
+kubectl expose deployment hello-web --type=LoadBalancer --port=8080
+minikube service hello-web
+```
+
+### 3. Scale the number of instances
+
+Now let's scale the application to 5 instances:
+
+```bash
+kubectl scale --replicas=5 deployment hello-web
+```
+
+Try to make few requests, you should see that the response will provide different hostnames.
+
+### 4. Update the image
+
+Now let's make some changes to our app and deploy a new version.
+
+Change `version` to `2` in `app.js` and rebuild a new image version with:
+
+```bash
+docker build -t hello-web:v2 .
+```
+
+update the deployment:
+
+```bash
+kubectl set image deployment/hello-web hello-web=hello-web:v2 --record
+```
+
+Wait few seconds and make some new requests. You should now see v2.
+
+
+### Cleanup
+
+Reduce all the pods to 0 (stop the app):
+
+```bash
+kubectl scale --replicas=0 deployment hello-web
+```
+
+Delete the deployment:
+
+```bash
+kubectl delete -n default deployment hello-web
+```
+
+Delete the service:
+
+```bash
+kubectl delete -n default service hello-web
+```
+
+You can finally stop minikube by running:
+
+```bash
+minikube stop
+```

12-scalability-and-architectural-patterns/08-scaling-an-app-on-kubernetes/app.js

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+import { createServer } from 'node:http'
+import { hostname } from 'node:os'
+
+const version = 1
+
+const server = createServer((_req, res) => {
+  res.end(`Hello from ${hostname()} (v${version})`)
+})
+
+server.listen(8080)

12-scalability-and-architectural-patterns/08-scaling-an-app-on-kubernetes/package.json

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+{
+  "name": "08-scaling-an-app-on-kubernetes",
+  "version": "1.0.0",
+  "description": "This example demonstrates how to implement peer-to-peer load balancing",
+  "type": "module",
+  "scripts": {
+    "start": "node app.js"
+  },
+  "engines": {
+    "node": ">=24"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "devDependencies": {},
+  "dependencies": {}
+}