Docker-Exercise1_NodeApp

Technologies

---

# Preparation

Copy the following files into a local directory on your system.

app.mjs

import express from 'express';
 
import connectToDatabase from './helpers.mjs'
 
const app = express();
 
app.get('/', (req, res) => {
  res.send('<h2>Hi there!</h2>');
});
 
await connectToDatabase();
 
app.listen(3000);

helpers.mjs

const connectToDatabase = () => {
  const dummyPromise = new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve();
    }, 1000);
  });
 
  return dummyPromise;
};
 
export default connectToDatabase;

package.json

{
  "name": "docker-start",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.17.1"
  }
}

Dockerfile

FROM node:14
 
WORKDIR /app
 
COPY . .
 
RUN npm install
 
EXPOSE 3000
 
CMD [ "node", "app.mjs" ]

---

# Build the image

Open a CLI and navigate into the folder you copied the files to.

Run:

docker build .

The output will give you a container Id. Something like

=> => writing image sha256:307e51e493e71a

---

# Run the container based on the image

Use the first few characters of the ID (copy enough so that it is unique) to run a container based on that image.

docker run -p 3000:3000 307e51e

You can then open the app on port 3000 of your local machine.

---

# Try using different ports

Specify different ports for both the exposed container port aswell as the host port.

# also edit dockerfile & app.mjs
# make sure host runs over port 3010
docker run -p 4010:3010 38c86108

---

# Make a change

Change the HTML output from the web server to something else. Run the container again and make sure you see the changes.

• Here you also have to rebuild the container

---

# Optimize the Dockerfile

Make sure that npm install only executes when the package.json file changes.

FROM node:14
 
WORKDIR /app
 
COPY package.json .
 
RUN npm install
 
COPY . .
 
EXPOSE 3010
 
CMD [ "node", "app.mjs" ]