Docker and Express Example

That is a very very basic example with expressjs and Docker. For beginners starting of with Node.js Servers. See this as an tutorial.

1. Node.js and using json-server

You need Node.js and npm installed on your PC. Create a new Directory and type: npm init To initialize your project. After that install the json-server package by typing into the console of your choice: npm install json-server Copy the mocks folder with the db.json into your project directory. Now add a new script to your package.json.

  "scripts": {
    "startMock": "json-server"
  },

And run your mock server by running npm run startMock and visit the localhost Address prompted in the console.

2. Write your Express server

Now install the express and axios package by running: npm install express axios And now add a src directory and an index.js file to your project.

Start of by adding:

const express = require('express')
const app = express()
const port = 8080

app.get('/', (req, res) => {
  res.send('Hello World!')
})

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`)
})

This initializes an express server and adds a Hello World Route. Now you can run it by ether running node src/index.js or add the following script to the script section of your package.json and afterwards running npm run start:

"start": "node src/index.js",

Visiting http://localhost:8080 will prompt you with an "Hello World" message.

After that you can add some more routes to try out expressjs. For example:

...
let counter = 0
...
app.get('/addition', (req, res) => {
  const zahl1 = req.query.zahl1
  const zahl2 = req.query.zahl2
  res.send(JSON.stringify(parseInt(zahl1) + parseInt(zahl2)))
})

app.get('/count', (req, res) => {
  counter++
  res.send('Aufruf: ' + counter)
})

After making changes you need to restart your application to have the changes applied. That can be automated by packages like nodemon.

3. Add a connection the the mock service

Make sure the Mock Server is running in its own shell and add the following code to your index.js:

const axios = require('axios')
let backendMock = 'http://localhost:3000/'
...
app.get('/diagnosis/:id', (req, res) => {
  axios.get(backendMock+req.params.id).then((e)=>{
    let diagnosisResult = "green"
    let msgs = []
    if(e.data.UAS.length > 2) {
      diagnosisResult = "red"
      msgs.push("To many UAS")
    }
    if(e.data.INITS.length > 2) {
      diagnosisResult = "red"
      msgs.push("To many INITS")
    }
    res.json({
      type: e.data.type,
      downstream: e.data.Downstream *  0.001 + " Mbit/s",
      upstream: e.data.Upstream *  0.001 + " Mbit/s",
      diagnosisResult: diagnosisResult,
      msg: msgs
    })

  })
})

You can test this function by for example calling http://localhost:8080/diagnosis/1

4. Dockerization

For this step you need Docker installed on your machine. Create a Dockerfile file in your Project and add:

FROM node:16-alpine

WORKDIR /app

COPY src /app/src
COPY node_modules /app/node_modules
COPY package.json /app

EXPOSE 8080
CMD ["npm", "run", "start"]

Now type docker build . -t <somename> into your console. By typing docker image after that you can see the image you just build. Now typing docker run -p <PORT>:8080 -d <somename> will run the Application on the provided port.