You might’ve heard about Docker. It might’ve sounded interested, but you didn’t know why you would use it, or it appeared scary. No fear, it’s actually quite straight-forward.

Firstly, you’ll need to download Docker itself. This is an application you will install and run like any other application. You even get a nice icon in your dock! :) You can even install this using Brew.

brew cask install docker

Why?

Docker is a way of defining a set of software for your application. This stops the whole “it works on my machine” that developers love to proclaim.

Getting Started

The main part of Docker is a Dockerfile. This contains the definition of your server and what you want to install. The Dockerfile contains instructions which should be run when the container starts.

A common starting point is to use a Docker image from the official repository

Images

The official images which can be used with no effort. There are common images for PHP, MySQL, nginx and node.

FROM node:12.11.1-alpine AS your_app

# Create app directory.
WORKDIR /usr/app/

# Copy package information and src files.
COPY package.json package-lock.json ./
COPY src ./src

# Install the packages needed for production.
RUN npm install --only=production

# Build the source.
RUN npm run build

# Remove the src.
RUN rm -rf ./src

EXPOSE 9000

CMD [ "npm", "start" ]

Compose

You can start your containers using the command line. This is OK with a simple set of instructions. A better solution is to define them using docker-composer.yaml files.

version: "3.7"

services:
    app:
        build:
            context: .
            dockerfile: Dockerfile
        image: your_app:latest
        container_name: your_app
        ports:
            - "9001:9000"

This will build your container using the Dockerfile you have created. It will use the files in the current directory using the context. It will also name your container so you can access it easily. Finally, it exposes port 9001 on your machine to port 9000 in the container.

Run

Finally, you can run everything using the following command;

docker-compose -f ./docker-compose.yaml up -d --build

This will start up your Docker containers using the docker-composer.yaml file. It will also --build the container from scratch, in case you already have an older version. Without the --build flag, it will use an existing build if one exists.

Common Commands

If you want to see what containers you have built and their status, you can run the following;

docker ps -a

To list all the images you have created or used;

docker images

If you want to get shell access to your container, then you would do the following;

docker exec -it your_app sh

Cleanup

Sometimes you want to cleanup the containers and images you have created. Below are a few commands which'll help with that.

docker stop your_app -t 0 # Stop your app.
docker rm your_app # Remove your app container.
docker rmi your_app # Remove your app image.