Preparing Dockerfile for an Express Web App

Create a directory for the express project
```
mkdir project
```
Go to the directory
```
cd project
```
Initialize a Node JS project. Answer all the question prompted on the terminal. Finally a package.json file will be created in the project/ directory
```
npm init
```
Install express
```
npm install express
```
Create a file for writing the express web app.
```
vi app.js
```

Write the code in app.js as below

const express = require("express");
const app = express();

app.get("/", (req, res) => {
	res.send({
		data: "HELLO WORLD"
	});
});

app.listen(5000, () => {
	console.log("START SERVER AT PORT 5000");
});

Create and write a Dockerfile as below

FROM node:18-alpine

# create "app" directory in the docker image
RUN mkdir app

# set "app" directory as the root working directory
WORKDIR app

# copy some files from the local machine into "app" directory in docker image
COPY app.js .
COPY package*.json .

# install dependencies at build stage
RUN npm install

# tell the develooper if this container will be run at port 5000/TCP
EXPOSE 5000

# run the program (web app) when the container is running
CMD node ./app.js

Build the image. Let say you are currently opening root directory where the project directory is located root is the parent directory of project)
```
docker build -t ricoputra/project-express project
```

Create a container from the image and set the PORT as well

docker container create --name ricoputra_project-express -p 5000:5000  ricoputra/project-express

Start/run the container

docker container start ricoputra_project-express

Open the web app on the browser by entering this url: localhost:5000/ and you will see the response below:
```
{
	"data": "HELLO WORLD"
}
```