Node.js example

Here is another example combining the different ideas and commands we've gone over. This example will walk through setting up an Express app with Node.js

References

• Node Docker Hub image: https://hub.docker.com/_/node
• Express install guide: https://expressjs.com/en/starter/installing.html

Figuring out what we don't know

Express requirements

Following the Express install guide, we know we'll need at least Node v18 (we'll just go with LTS though). We'll also need npm (Node's package manager) to install and initialize Express.

Node image

Before we get too far, we need to actually find a base image that we can go off of. A quick search on Docker Hub leads us to the official Node Docker image. We can use this as our base.

docker pull node:lts

With the node:lts image pulled down, we can do a few quick tests in the image to see what we have to work with:

# Check node version
docker run --rm -it node:lts node --version

# Check npm version
docker run --rm -it node:lts npm --version

# See if the is a user with a home directory we can use
docker run --rm -it node:lts ls -al /home
docker run --rm -it node:lts whoami # root, though there is a node user we can use

Node and npm are both installed and accessible and the versions meet Express's requirements. There is a node user that we can use to execute commands in the container.

Install Express

For this example, we're going to create a new directory for our Django app to live in

mkdir express && cd express

Let's try to initialize the package with the node user and see what happens. I'm going to set the working directory to /home/node/app and create a bind-mount volume for our express directory to be mounted to the /home/node/app directory in the container.

docker run --rm -it -w /home/node/app -v ./:/home/node/app --entrypoint=npm --user node node:lts init

And here we can install express

docker run --rm -w /home/node/app -v ./:/home/node/app --entrypoint=npm --user node node:lts install express

Setup Hello World example

Still following the Express guide, we can add the Hello World example implementation.

We can create a app.js file in the express directory.

touch app.js

Then we can write the following content to the file:

const express = require('express');
const app = express();
const port = 3000;

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

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

Running the express server

We can see that the port that the app will be listening on is port 3000, so we can write a docker run command to test this out.

docker run --rm --init -w /home/node/app -v ./:/home/node/app -p 3000:3000 --user node node:lts node app.js

INFO

I added the --init flag here because the container wasn't responding to ctrl+c signals.

You should be able to see "Hello World" in your browser now if you go to http://localhost:3000

Setting up docker compose and shell script files

We can start making our lives a bit easier by setting up a docker compose file, so we don't have to remember all of these flags that need to be included during a run command, then set up shell scripts to wrap the docker compose commands after that.

touch docker-compose.yml

The docker-compose.yml file will have the following contents (derived from all the flags that were being used in the previous docker run command)

services:
  node:
    image: node:lts
    user: node
    ports:
      - 3000:3000
    init: true
    working_dir: /home/node/app
    volumes:
      - ./:/home/node/app

Create the bin directory as well as two shell scripts that help us wrap running npm and any command in the node container service. The shell scripts need to be executable, and we can make symlinks to them in the root of the express directory.

mkdir -p bin
touch bin/npm.sh bin/node.sh
chmod +x bin/*.sh
ln -s bin/npm.sh ./npm
ln -s bin/node.sh ./node

Contents of the npm.sh file:

#!/bin/bash

mkdir -p node_modules

docker compose run --rm --service-ports --entrypoint=npm node $@

Test to make sure the pip shell script works:

./npm install

Contents of the node.sh file:

#!/bin/bash

mkdir -p node_modules

docker compose run --init --rm --service-ports --entrypoint=node node $@

Test to make sure the node shell script works:

./node app.js