Simple Docker Container Tutorial

Docker is all the rage. I cover it more in depth on this post but I wanted to show you how to use the absolute basics of Docker.

Let's get started.

Requirements

Windows 10 Professional docs (seriously; you need Virtual Machine support and Windows 10 Pro has it)
macOS docs

1. Create a Docker Hub account here

2. Install Docker Desktop here

3. After install, be sure to login to Docker Desktop

4. Verify Installation

Open Terminal (Mac / Linux) / PowerShell

docker --version

You should see something like:

Docker version 19.03.2, build abc123

5. Your first Docker project

Find a place for your project:

cd path/to/your/dev/folder

Now that we're here, let's create our first Dockerfile

touch Dockerfile

Dockerfile is the convention and best practice name. No extension.

6. Dockerfile 101

A docker file is a standardized way for Docker to build your Docker Image. A Docker Image is essentially an operating system and typically a linux one. The Docker Images can be moved around easily and repurposed for a variety of use cases.

Let's edit our Dockerfile now:

# In path/to/your/dev/folder/Dockerfile
# Base Image
FROM python:3.6

RUN apt-get update && apt-get install -y --no-install-recommends \
        python3-setuptools \
        python3-pip \
        python3-dev \
        python3-venv \
        git \
        && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

EXPOSE 8000

CMD python -c "print('hello world')"

What's going on here?

Remember, capitalization is very important.

FROM

FROM

is going to build your image from another pre-existing image. This can get pretty advanced so for now, we just use a good python 3.6 image.

RUN

RUN is a command that allows you to do any bash shell command you'd do normally. In our case, we just do some basic system updates and basic installs.

EXPOSE

EXPOSE

allows your docker image to have a port or posts exposed to outside the image. This is important for web applications and software you want to receive requests.

CMD

CMD

this is the final command your docker image will run. It's typically reserved for something like running a web application.

COPY

COPY

copy is another command we haven't yet added to our Dockerfile. This will allow you to copy local files to your Docker image.

6. Commands for Docker

$ docker build -t <your-tag> -f Dockerfile .

$ cd path/to/your/dev/folder
$ ls
Dockerfile

Now run the build:

$ docker build -t hello-world -f Dockerfile .

This will build your actual image. It might take awhile (5-15 minutes) depending a number of factors. After you build it 1 time, the future builds might not take as long :).

-t portion means "tag" and you can add your own tag name I used hello-world since this might be your first time using Docker. When in doubt, include a tag.
-f is the path to the Dockerfile you're going to use to build your image.

$ docker images

Running this command anywhere on your system, assuming Docker Desktop is running, will show you all of the images your system has. It will also have the python 3.6 image we grabbed in our Dockerfile. Pretty cool right?

Pro tip, to remove all of these images just run docker rm $(docker ps -a -q) then docker rmi $(docker images -q)

$ docker ps -a

This will show you all of the containers that are currently running. After we build our image, we need to run it as a container.

$ docker run -it <your-tag>

This creates a "container" from your tagged image. In other words, a container is an instance of an image.

Following the example above, you'll run:

$ cd path/to/your/dev/folder
$ ls
Dockerfile

Now run the build:

$ docker run -it hello-world
hello world

If you copied our Dockerfile exactly, you should see the response from docker run -it hello-world as simply hello world. This means your image is working!

Tip: You can actually run docker run -it <your-tag> anywhere on your system and it should run your project.

$ docker run -d -it <your-tag>

If you add -d it will run in the background. This has it's own section because running your container in the background can cause conflicts with other containers using the same port.

To stop a background running container, you can first list all running containers:

$ docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                    PORTS               NAMES
5966a461fa9d        hello-world         "/bin/sh -c 'python …"   3 seconds ago       Exited (0) 1 second ago                       thirsty_cori

$ docker stop <your-container-id>

Above we ran $ docker ps -a. This showed us our docker container had an id of 5966a461fa9d. We can now stop and remove that container

docker stop 5966a461fa9d
docker rm 5966a461fa9d

6. Bash Shell in a Docker Image

docker run -it <your-tag> /bin/bash

That's it. You now have access to your docker container's bash shell.