TypeOfNaN

How to Serve a Node App in Docker

Nick Scialli October 17, 2020🚀 4 minute read

If you're enjoying this blog, please consider one or both of the following:

Serving a node application in Docker is actually fairly simply. In this post, we’ll do so using only a six-line Dockerfile!

Create a Sample App

For our proof-of-concept, we’ll create a sample node app in a new directory. Let’s quickly put one together.

Create app directory

First create a node-in-docker directory and cd into it.

mkdir node-in-docker
cd node-in-docker

initialize npm project with defaults

Next, initialize an npm project. The -y flag will initilize with default settings.

npm init -y

Add express.js and simple code

Our app will be an express app.

npm i express

Create an index.js file with some simple home route handling.

touch index.js

With the following code:

const express = require('express');
const app = express();
const port = process.env.NODE_SERVER_PORT;

app.get('/', (req, res) => res.send('Sample node app!'));

app.listen(port, () =>
  console.log(`Example app listening at http://localhost:${port}`)
);

Note that our port will come from a NODE_SERVER_PORT environment variable.

Test the app

Let’s test that our app looks good before we add any Docker code. We can do this by using node . and remembering to include our environment variable.

NODE_SERVER_PORT=3000 node .

Now if we navigate to http://localhost:3000, we should see our sample app.

sample app

If you see this, we’re now ready to dive into docker land!

Add Docker

In this minimal example, all we’ll need is two files:

  1. Dockerfile
  2. .dockerignore

The Dockerfile will be the blueprint for creating our Docker image and the .dockerignore will be used to tell Docker to ignore the node_modules folder when building the image.

.dockerignore

The .dockerignore file is pretty easy, let’s just throw the string node_modules in there.

echo "node_modules" > .dockerignore

Dockerfile

The Dockerfile is a bit more complex, but not by much!

Let’s first create the file

touch Dockerfile

And now here’s the magic. Read the comments to see what’s going on.

# Use the node v10 image
FROM node:10
# Set working directory
WORKDIR /app
# Copy contents of current directory into working dir
COPY . .
# install node modules
RUN npm i
# Set the node server port to 3000
ENV NODE_SERVER_PORT=3000
# Containers start the app by running node .
ENTRYPOINT ["node", "."]

Build the Docker image

Let’s build the docker image based on the instructions in our Dockerfile!

We will use the tag (-t) node-server and our build context will be the current directory (.).

docker build -t node-server .

Run a container

Now we can create and run a container based on our node-server image! To so so, we’ll use the following options:

  • --rm to cleanup old instances
  • -it flags for terminal behavior
  • Expose container port 3000 on port 3000
docker run --rm -it -p 3000:3000 node-server

Now if everything works, we should be able to go to http://localhost:3000 and see our sample node app!


Nick Scialli

Nick Scialli is a software engineer at the U.S. Digital Service.

Subscribe to the mailing list!

If you like what I post here, please sign up to get updates and code insights in your inbox. I won't spam you and you can unsubscribe any time!

Powered by Buttondown.