Setting up Docker (basics)

I have recently starting using Docker for a few projects, and wanted to share how to get it set up on your machine.

In this post I describe how to download Docker, get it configured on your machine, and start running your first Docker file.

1. Downloading and Installing Docker

Head over to the Docker website and install the Docker version for your machine. I currently use the Apple version, but Docker is multi-platform, so can run containers on any system.

I would also recommend downloading Docker Desktop. It makes visualizing and interacting with images & containers easier, but isn’t necessary. It provides a personal plan for free.

2. Using, Creating and Building an image

In a terminal, you can run the command docker run hello-world. This will run an image called “hello-world”. Docker will look for an image named “hello-world” on your local machine, and if it can’t find it, it will download it online from Docker Hub. There you can download and run different images like python, ubuntu, postgres and many more.

To create a new Docker image on an existing project, in your root folder, create a new file called Dockerfile. The format is as follows:

INSTRUCTION arguments

So an example of a nodeJS image would look like this:

## specifies the base image, in this case,
##using node version 16 as base image
FROM node:16

#Setting a working directory named '/app'
WORKDIR /app

#Copy over a file into the working directory
#(you can use * as a wildcard to match any text)
COPY package*.json /app
##Copy my current project's src folder into the
##working directory app/src folder
COPY src /app/src

##Running `npm install` installs all dependencies needed
##for the application
RUN npm install
##Here I am binding the port 5200 to the host system and the
##port 80 to the Docker container.
EXPOSE 5200:80
#provides a command with arguments to be used
CMD ["npm", "run", "serve"]

You can now build this image with docker build -t NAME-IMAGE ., the -t flag allows you to name your image, and the period specifies the current directory.

3. Running a container/image

To run it, use docker run -d IMAGE-NAME, the -d flag specifies it running in detached mode. Great! Now your image is now running in a container. In my case, I can go to a browser, navigate to localhost:5200 and see my application running.

4. Docker Desktop, Docker Compose, and Docker Hub

Even though I know the command line arguments for running a Docker image, I prefer using Docker Desktop since it is a great interface for setting ports and environment variables. If you use a env. file in your project, and it is included in your .gitignore, unfortunately Docker won’t include it (or any file in the .gitignore) in the image. Even with specifying environment variables in Docker Desktop, it can get tedious if you have many environment variables.

A solution for this is Docker Compose (which should already be downloaded with your download of Docker Desktop). Docker Compose can include those environment variables in the image when writing the docker-compose.yml file (I will write a complete post on Docker Compose later on).

My last note is if you use Docker Desktop and/or work on a project that multiple people use, I would highly recommend creating an account with Docker Hub. There you can create Docker repositories, and share Docker images with other collaborators for distributing images easily.