Run Express in Docker

Docker has emerged to be a standard of building and deploying applications. The best part of docker is it gives a complete abstraction over the environment or OS. There are plenty of material on what docker is, or how it works, however, what we are going to discuss over here is to how to put your nodeJS express app in docker container.

First things first

What we need

1. A computer with docker installed on it. Preferably linux/mac.

Windows has its challenges to run docker desktop, especially win10 Home editions, so you need to really go through the documentation in docker site before installing docker.
WSL too is dependent on Win10, so go as per the documentation given in docker website.

1. A Express Application to play with.

I have an express app, created out of express generator hosted on github which i'm going to be using for this exercise.
https://github.com/tirthaguha/card-deck-test
The code on this repo runs on PORT 4000, and exposes API
http://localhost:4000/card-deck/shuffle. This repo makes a call to external APIs, so your system should be enabled to make API calls.

Enough talk, run me the docker

If you are using my repository, don't run npm install. :-O. Lets not waste time here running a simple express app, lets just go straight into using docker.

Create the Dockerfile

Within the repository, create a Dockerfile, and a .dockerignore file, next to package.json

touch Dockerfile
touch .dockerignore

Lets open Dockerfile and add these entries into it.

FROM node:12-slim

# create a directory in your docker image
WORKDIR /app

# install dependencies
COPY ./package*.json ./

# run npm install. you just need the runtime dependencies here
RUN npm ci --only-production

# Copy the rest of the code
COPY ./ ./

# Expose the port, on which your application is running
EXPOSE 4000

# Run the code
CMD [ "node", "./bin/www" ]

Save this Dockerfile.

As you would have guessed already, .dockerignore contains the entries which will be ignored when you're copying all your code on the docker image. Enter the following in the .dockerignore file and save it.

node_modules
npm-debug.log

Build the image

Build your first docker image

docker build -t card-deck-test .

Check the image in your local registry

docker images

It should give you an output like

REPOSITORY       TAG      IMAGE ID
card-deck-test   latest   aaaa1111dddd1111

Run the image

docker run -p 4000:4000 -d card-deck-test

The express application is now running on port 4000 in the container, and the container is exposing port 4000. So to summarise, you can now see your application running by opening
http://localhost:4000/card-deck/shuffle on your browser.

What next

Play around with docker

1. Run multiple containers simultaneously

docker run -p 4000:4000 -d card-deck-test
docker run -p 4001:4000 -d card-deck-test
docker run -p 4002:4000 -d card-deck-test

then open all of them on browser
http://localhost:4000/card-deck/shuffle
http://localhost:4001/card-deck/shuffle
http://localhost:4002/card-deck/shuffle

1. See the containers running

docker ps -a

1. Stop the docker container

docker stop [CONTAINER_ID]

1. Remove the docker container

docker rm [CONTAINER_ID]

Happy Containerising!