Create and deploy a NodeJS Express app with Docker

I’ll show you a stupid fast and simple way to create an express app with NodeJS, then deploy it with Docker. All you need is a simple text editor.

Install NodeJS & Docker

Install node with n:

npm i -g n
n latest

Install Docker by pulling out the appropriate build from https://docs.docker.com/engine/installation/.

App setup

Let’s now get our express app setup. Create a new directory and initialize your package.json file:

mkdir test && cd test
npm init -y

Let’s now install express:

npm i -S express

And set your main npm start script. Change the line that reads:

"test": "echo \"Error: no test specified\" && exit 1"

to this:

"start": "node index.js"

App coding

And we’ll create our index.js file. We’ll keep it simple ;)

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

app.get('/', (req, res) => {
  res.send('Cleveland Cavaliers are world champs!');
});

app.listen(3000, () => console.log('Server running'));

Make sure it works by executing:

npm start

Now, when you visit http://localhost:3000 on your local machine, you should see something that will make Golden State Warriors fans cry.

Hint: Check out nodemon so you can make changes to your app code and not have to restart node on every change.

Docker setup

Now that our app is running, let’s setup our Docker config.

First, create a .dockerignore file containing one line:

node_modules

We want to exclude our local packages from Docker, as these will be installed at build time.

Now, we’ll create a new file named Dockerfile with the following contents:

FROM mhart/alpine-node

WORKDIR /src

COPY package.json .
RUN npm i

COPY . .

EXPOSE 3000

CMD ["npm", "start"]

We’ll be using the mhart/alpine-node base image, as these is a super tiny NodeJS instance built on the minimalistic Alpine linux distribution. The output of my build was about 55MB. and it took less than a minute for the initial build. Subsequent builds took about one second =)

The Docker instructions are pretty simple. We just copy over the package.json file, install our npm modules, then copy our app over and run npm.

Let’s build our production image:

docker build -t test .

Now, we can run our our image to test it out. We’ll map port 3000 from our host to container, and run in daemon mode so it keeps running in the background:

docker run -p 3000:3000 -d test

Now, when you visit http://localhost:3000, you can see the same output as before, but things are now running from your Docker container. You can now push your Docker image to a private repository or build service, then deploy to production, and know there are no dependencies, build issues, or anything else to worry about. It will just work.