How to run Node app in Kubernetes

Summary

We can follow these main steps to run our Node app in Kubernetes. In this post, I use Docker as the container runtime for Kubernetes.

1. Write the app in Node.js.
2. Write a Dockerfile and build a Docker image from it.
3. Push the image to Docker Hub.
4. Use the image above to create a Kubernetes Deployment.

Step 1: Write the app in Node.js

To make it simple, I wrote a web app using Express, which has only one API Endpoint:

const express = require("express");
const app = express();
const port = process.env.PORT || 3000;

app.use(express.json());
app.get("/greeting", (req, res) => res.send({ message: "hello" }));

app.listen(port, () => console.log(`server listens on port ${port}`));

Step 2: Build a Docker image

We can use the Dockerfile below to instruct Docker to build a container image for our app:

FROM node:16-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
CMD [ "node", "server.js" ]

We also need a .dockerignore file so Docker will not copy unnecessary files to our image.

node_modules
.DS_Store
npm-debug.log

Now let's build the image by running this command. (<your username> is your username on Docker Hub)

> docker build . -t <your username>/myapp

Step 3: Push the image to Docker Hub

The image is now created. Assume you have already had a Docker Hub account. You can log in using:

> docker login

We can now push it to Docker Hub:

> docker push <your username>/myapp

Step 4: Run the app in Kubernetes

I use minikube to set up a local Kubernetes cluster for testing purposes. If you are interested, you can follow the instruction on its homepage to set up on your machine.
So now we have a Docker image on Docker Hub, we can use it to create a Deployment:

# file deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: myapp
          image: <your username>/myapp
          ports:
            - containerPort: 3000

Create the deployment by executing

> kubectl create -f deployment.yml            

Check if your pod is running

> kubectl get pod -l app=myapp
NAME                                READY   STATUS    RESTARTS   AGE
myapp-deployment-54865d44bf-h8t9r   1/1     Running   0          18m
myapp-deployment-54865d44bf-llsfs   1/1     Running   0          18m
myapp-deployment-54865d44bf-p7dkq   1/1     Running   0          18m

Check the log:

> kubectl logs myapp-deployment-54865d44bf-h8t9r myapp
server listens on port 3000