README.md

Packages (Docker)

We will work today your Github repository. The repository with Python code, you have created last time:

|- .github/workflows
|- hello_world/
|- test/
|- main.py
|- Makefile
|- README.md
|- requirements.txt
\- test_requirements.txt

Preparation

1. Check whether the application works locally following the steps from the project README.md.

   make test
   make lint
   make run

   curl 127.0.0.1:5000/

2. Please verify your github flow works.

Packaging

1. What is the dependency hell?

2. What are different approaches to address it?

   • How does Python or NodeJS solve it?
   • Linux distributions, e.g., deb or rpm? What is snap and what the difference is?
   • How did we address it on the cloud?
   • What did Docker bring to the table?

3. Add to your project Dockerfile:

   FROM python:3
   
   ARG APP_DIR=/usr/src/hello_world_printer
   
   WORKDIR /tmp
   ADD requirements.txt /tmp/requirements.txt
   RUN pip install -r /tmp/requirements.txt
   
   RUN mkdir -p $APP_DIR
   ADD hello_world/ $APP_DIR/hello_world/
   ADD main.py $APP_DIR
   
   WORKDIR $APP_DIR
   CMD FLASK_APP=hello_world flask run --host=0.0.0.0

4. Let's see whether we can build the docker image for our app:

   sudo docker build -t hello-world-printer .

   # please verify whether you can see your image
   sudo docker images 

   Notice: if your application is simple, you can verify whether it starts during the building phase. Just change CMD to RUN for testing

5. If it works, please add a dedicated target in your Makefile:

   docker_build:
   	docker build -t hello-world-printer .

   and test it.

6. Docker provides us commands to run the application with one command:

   sudo docker run \
       --name hello-world-printer-dev \
       -p 5000:5000 \
       -d hello-world-printer

7. To check whether it runs properly:

   # does it run?
   sudo docker ps
   
   # if you do not see your docker running:
   docker ps -a

   # does it respond?
   curl 127.0.0.1:5000/

   # what the logs say
   sudo docker logs hello-world-printer-dev

8. We might need to check the Docker from within:

   sudo docker exec -it hello-world-printer-dev /bin/bash
   
   
     root@b7:/usr/src/hello_world_printer# 

9. Time to add another target to our Makefile:

   docker_run: docker_build
   	docker run \
   		--name hello-world-printer-dev \
   		-p 5000:5000 \
   		-d hello-world-printer

10. How to restart a Docker:

    sudo docker stop hello-world-printer-dev 
    sudo docker rm hello-world-printer-dev
    sudo make docker_run

11. The next step is to build your package (in our scenario a Docker Image) as a part of your CI/CD process (see docs). Please add at the end of your workflow file:

      # ...
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
       - name: Build and export to Docker
         uses: docker/build-push-action@v2
         with:
           context: .
           load: true

12. We should also publish our Docker Image to a repository. hub.docker.com is the most popular one:

    1. Create an account on hub.docker.com.
    2. Following the example from docs publish your image.

Advanced topics

• Run your Docker and mount the source code from your workstation to the Docker, so you can faster iterate. No need to rebuild your image, you can just restart the Docker:

  sudo docker run \
       --name hello-world-printer-dev \
       -v $(pwd):/usr/src/hello_world_printer/
       -p 5000:5000 \
       -d hello-world-printer

• Does my Dockerfile follow best practices? We have a linter for that:

  docker run --rm -i hadolint/hadolint < Dockerfile
  
  # search & lint!
  find . -iname Dockerfile | xargs -I {} bash -c "echo {}; docker run --rm -i hadolint/hadolint < {}"

• Security? Does the Docker image contain outdated packages? I recommend trivy.

  trivy image hello-world-printer

Ideas for Python Practice

1. Add XML output for your hello printer app.

2. Let the client, provide her or his name as a GET argument:

   curl '127.0.0.1:5000?name=apolonia&output=json'

   add relevant tests.

3. Generate JSON output with the built-in json library (do not forget about the tests):

   import json

4. Generate XML output with lxml (do not forget about the tests):

   pip3 install lxml

   Hint: see this post on stackoverflow.

5. Execute the flask app with gunicorn.