My notes on Docker









#blog #docker

The documentation at is really good and I would recommend reading through the first 2 parts. This post is mostly just the tutorial rehashed.

”Docker” is a collection of applications that help package and distribute applications. Installing Docker on a machine is similar to installing a Java Virtual Machine. However, where a JVM abstracts the CPU, Docker abstracts an entire system.

Docker (for the most part) is a comprised of 2 applications: the Docker daemon and the Docker CLI. You will need at least the Docker CLI installed on your local machine, and the Docker daemon could be running else where. Having the daemon installed elsewhere is perhaps something you don’t need to worry about to start with though.

Docker used to be only truly a Linux application, as it relied on features available in the Linux kernel. When installing “Docker Desktop” for Windows or Mac, you are installing an application that is managing a Linux virtual machine, which itself is being used to manage virtual machines…

There is however now native Windows support.


For Windows, Microsoft Hyper-V is required to run Docker Desktop. When Hyper-V is enabled, VirtualBox no longer works.

Instructions for getting Docker installed onto your machine can be found on the docker website.

Because Docker uses Linux kernel features, Docker doesn’t currently work directly on WSL. However, WSL2 has been released, which ships with an actual Linux kernel. It is only available in Windows builds 18917 and higher.

I currently have WSL installed, so I followed the WSL install blog post. However, I had issues with my WSL Docker CLI communicating with the Windows daemon. The work around I’m using involves running socat in a docker container:

docker run -d --restart=always -p -v /var/run/docker.sock:/var/run/docker.sock  alpine/socat  tcp-listen:2375,fork,reuseaddr unix-connect:/var/run/docker.sock

First container

This is the same steps as but with one of my repos.

Defining a Dockerfile

Clone the project from GitHub

git clone
cd bus-stop

This is a single page web app that displays the current bus information for the bus stop outside the my office.

In the repo there is a file called Dockerfile. This is similar in concept to a Makefile and is what is used to define the resulting Docker image.

FROM nginx:latest

COPY index.html /usr/share/nginx/html
COPY main.js /usr/share/nginx/html
COPY style.css /usr/share/nginx/html


CMD ["nginx", "-g", "daemon off;"]

FROM specifies which image to use as the parent image. The important concept here is that this is also just a Docker image, which could be used in a container. Images can be found on the Docker Hub. The Dockerfile for nginx can be found on GitHub.

COPY copies a local files into the new Docker image.

EXPOSE opens up a port.

CMD runs a command in a running container.

Building an image

You can now build an image from this Dockerfile using the command

docker image build -t bus-stop .

docker image build is the build command, while -t bus-stop “tags” our resulting image. This is important because you can view images already built on your machine using

repos/bus-stop$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
bus-stop            latest              ab443971cc03        2 hours ago         127MB
nginx               latest              2073e0bcb60e        3 weeks ago         127MB

Untagged images will just show up as

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
<none>              <none>              0e63f6aabdc9        22 seconds ago      154MB

Building an image can be seen synonymous with building or compiling source code.

Once an image is build, you can use it locally. Images can also be exported with

docker save bus-stop > bus-stop.tar
# Or equivilantly
docker save --output bus-stop.tar bus-stop

Then loaded with

docker load < bus-stop.tar
# Or equivilantly
docker load --input bus-stop.tar

Starting a container

Once the image has been build, we can run it in a container.

docker container run --publish 8000:80 --detach --name bus-stop bus-stop

docker container run is the command run a new container. --publish 8000:80 forwards traffic from port 8000 to the Docker containers port 80. --detach forks the process so it can run in the background. --name name’s the running container, without this the container gets a random name generated by the Docker daemon.

Opening http://localhost:8000/ you should see the web app which is being served by Nginx.

In addition to starting this container, it has also been added to the list of containers managed by your instance of Docker.

You can view all instances with

repos/bus-stop$ docker container ls --all
CONTAINER ID        IMAGE               COMMAND                  CREATED              STATUS                          PORTS                      NAMES
fcab388de37b        bus-stop            "nginx -g 'daemon of…"   About a minute ago   Exited (0) About a minute ago                              bus-stop
15d251abc371        alpine/socat        "socat tcp-listen:23…"   26 hours ago         Up 9 hours            >2375/tcp   exciting_cerf

To stop the container you can use

docker container stop bus-stop

And to remove the container

docker container rm bus-stop