Docker
Watch the video here
Prerequisites
- Install Docker Desktop
- Note that this is the most environmentally complex pre-req we’ve used so far in this course. If you need to spend your non-zero day on setting this up that’s fully appropriate. We will be using Windows 10 Professional for the demonstrated environment.
- Install Visual Studio Code
Loose Agenda
Play with Docker Create container images
Step by Step
Setup playground
Create a directory for playing Open a powershell terminal to the relevant directory
Pull an image from Docker Hub
docker pull alpine
Review images on local system
docker images -a
Run an image
Let’s run the container image
docker run alpine
Note that nothing happened. Let’s check the running containers
docker ps -a
Let’s clean up our environment and try that again
docker rm $(docker ps -aq)
docker run -it alpine
the -it argument tell docker that you want to attach to the container process that’s starting up. Read more on the arguments we’ll be using in Docker Documentation. You should now see the following which indicates you’re attached to an Alpine linux distribution environment.
/ #
Try running some linux commands
ls
top
CTRL+C to exit the top process then type exit to exit the container. Note that we now need to clean up the container as it is left in a stopped state.
See the containers
docker ps -a
Clean up
docker rm $(docker ps -aq)
Going forward we will use --rm to tell Docker to clean up the container on exit.
Create Dockerfile
Open Visual Studio Code to our directory for today’s exercise.
Create a new file named Dockerfile and open it for edit.
Enter the following
FROM alpine
Now let’s navigate back to our terminal instance. Verify that our terminal is in the same directory that our dockerfile is in.
Note the Docker Documentation section contains Dockerfile insights.
Run a Dockerfile
Run
docker build -t non-zero-image .
This will build our image and tag it as non-zero-image. Verify with the docker images command.
Now let’s run the image as before but with our new tag.
docker run -it --rm non-zero-image
We can now iterate on our Dockerfile and rebuild it.
Revisit Previous Exercise with Docker
Let’s grab the code from our Python Flask exercise and create a Dockerfile for it.
If you don’t readily have the app.py and motd.txt then go ahead and clone it to another directory. For today’s exercise we will simply drag those files into our new play directory, though it would be equally viable to store the Dockerfile we’re making in that repository.
Once we’ve added motd.txt and app.py to today’s directory, let’s adjust the final line of the app.py file
Change
app.run()
to
app.run(host="0.0.0.0")
Now let’s adjust our Dockerfile as follows
FROM python:3.9.1-alpine
ADD . /code
WORKDIR /code
RUN pip install flask
EXPOSE 5000
CMD ["python", "app.py"]
We’ve changed the base image to one which has python already installed, then we’ve pulled our code into the image, installed our prerequisites (flask) and indicated that we want to run app.py as the startup activity. Let’s build and run the image.
docker build -t non-zero-image .
docker run -it --rm -p 5050:5000 non-zero-image
Open your internet browser of choice and navigate to localhost:5050/motd
You should see Happy Non-Zero Month!
Congrats on your Non-Zero day!