I've used Docker quite a bit but I haven't really dived into configuring my own dockerized app. I recently needed to build a quick proof of concept with a React app and needed to share it easily without worrying too much about build dependencies or anything of the sort. So here's a quick guide on dockerizing an app created with create-react-app.

The guide

I'll assume you already have a CRA app created. If you've never used create-react-app, I recommend checking out the docs here. This tutorial will work from the top down and both the Dockerfile and docker-compose.yml files will be at the end in full.

Create a Dockerfile at the root of your application. First we need to figure out what base image we're going to use. I'm biased towards the Alpine based ones cause those are lite and quick to spin up. So we'll use node:current-alpine3.10. This tells Docker to pull the current alpine 3.10 image from Dockerhub.

FROM node:current-alpine3.10

Next we'll need to set the working directory, where the app will be "put", dependencies will be installed in, and our run command to run.

WORKDIR /app

We'll setup the PATH to ensure that the node_module binaries are accessible globally.

ENV PATH /app/node_modules/.bin:$PATH

Next is probably the part that confused me the most when working with Docker. We have to copy over critical files to ensure that the container knows where to get our dependencies and how to build them all. This step needs to be done explicitely and not make use of a volume due to the fact that it'll overwrite dependencies if you're not careful.

COPY package.json ./
COPY yarn.lock ./

This ensure that just the dependency and depenency lock file are both available to the container. We could just copy over the node_modules folder from our local machine into the container, but it's likely that something will break cause sometimes certain modules are built differently for different targets.

Next we'll tell the container to install the dependencies.

RUN yarn install

Finally we'll tell the container to execute our build/run command. This command is important cuase it represents the "main" process for our image which is why this is CMD instead of RUN.

CMD ["yarn", "start"]

Before we move on we'll need to go ahead and setup the docker-compose.yml and .dockerignore files to ensure everything runs as inteneded. The convience of docker-compose is that you don't have to pass 100 args to the Docker CLI.

Lets setup the .dockerignore first.

node_modules
build
.dockerignore
Dockerfile

This ensures that Docker doesn't use the node_modules or build directory in the volume we create in the docker-compose.yml. Not ignoring the node_modules directory will result in our previously installed dependencies being overwritten by what's on our local machine. So lets make sure the container uses the dependencies it has.

Ok now for the last bit, the docker-compose file. Here we declare a version, the service/container_name and then pass the actual configuration. We need to tell docker to use the current directory as it's main "context" and subsequently use the Dockerfile in that directory.

version: '3.3'

services:
  wc-concept:
    container_name: wc-auth-concept
    build:
      context: .
      dockerfile: Dockerfile

Now we have to define Volumes. Volumes can be used for persistant reference between Docker container builds. Since each container is meant to be spun up and destroyed with no lingering side effects, volumes represent a way to tell Docker about persistant information. This can be a database file or in our case, the code. This tells docker to reference the code in . which is our local project directory as the code in /app which is the directory of the application code in the container. We also add a node_modules volume to ensure we don't have to constantly download them whenever the container spins up.

version: '3.3'

services:
  wc-concept:
    container_name: wc-auth-concept
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      - '.:/app'
      - '/app/node_modules'
    ports:
      - 3001:3000
    environment:
      - CHOKIDAR_USEPOLLING=true

There's 2 more things in the above example. First we define the port to expose out of the container and forward it to a port on our local machine. My project runs on 3000 by default, which is what Docker knows about. We'll expose port 3000 from the container and forward it to port 3001 on our local machine. The format is local_port:container_port. Finally we tell Docker to poll the volumes for changes so we can take advantage of webpack-dev-server or hot reloading.

Now you can just run docker-compose up, with the optional -d flag which is "detached" mode and it will run in the background instead of outputting to the terminal, and visit localhost:3001.

Here's all the code for all 3 files in one place for reference.

Dockerfile

FROM node:current-alpine3.10

WORKDIR /app

ENV PATH /app/node_modules/.bin:$PATH

COPY package.json ./
COPY yarn.lock ./

RUN yarn install

CMD ["yarn", "start"]

.dockerignore

node_modules
build
.dockerignore
Dockerfile

docker-compose.yml

version: '3.3'

services:
  wc-concept:
    container_name: wc-auth-concept
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      - '.:/app'
      - '/app/node_modules'
    ports:
      - 3001:3000
    environment:
      - CHOKIDAR_USEPOLLING=true

This worked just fine for my purposes. I'm sure there's more to be done to make this Docker configuration way more robust. Enjoy.