Roman Numerals CI/CD Kata

The goal of this kata is to practice setting up a continuous integration / continuous delivery system.

We start with my solution to the Roman Numerals kata (also known as the Reverse Roman Numerals kata). We've added on a simple web UI.

You will take this simple web app and set up a continuous delivery pipeline to run it in "production."

Here are the steps:

Fork this repository

You will need your own Roman Numerals repository. To fork this repository:

• Visit https://github.com/rkasper/roman-python.
• Click the Fork button.
• In your GitHub account, visit the forked repository you just created. Note the URL of your Roman Numerals repository.

Clone your Roman Numerals repository

• In PyCharm Professional, create a new project from version control.
  • Select File / Project from Version Control....
  • For Version Control, select Git.
  • For the URL, copy-paste the URL of your Roman Numerals repository.
  • Click the Clone button.

Make sure the app runs on your machine

• If you notice an error like no such file or directory: venv/bin/python, then install a new Python virtual environment. One way to do this is to select Preferences / Project / Python Interpreter. Click the gear icon, and add a new virtual environment. On my machine, PyCharm finds the python3 executable.
• If you notice an error like no such file or directory: venv/bin/behave, then either:
  • Open file requirements.txt and follow the instructions at the top of the editor window, or
  • Type this inside a terminal in your project's root directory: $ venv/bin/pip install -r requirements.txt
  • Run all the tests. In the Project browser at the top-left of the IDE, right-click app / test. Select Run 'Python tests in test...'. Confirm that all the tests are green.
    • 🤔 Open each file in the test directory. What does each file do?
  • Run the web app. In the Project browser, right-click file flask-app.py. Select Run flask-app. Visit http://127.0.0.1:5000 and play with the web app.
    • 🤔 Open file flask-app.py. How does it work?
    • 🤔 Where is the UI code for the web app?
    • 🤔 Where is the Roman numerals business logic?
    • 🤔 Is there any storage?
    • 🤔 Are there any other files? What does each file do?

Set up your continuous delivery pipeline

We'll use DigitalOcean App Platform, a super-simple way to set up a continuous delivery pipeline and deploy an application.

• Login to DigitalOcean, either using your own account or using an account provided by your instructor.
  • If you create a new account, DigitalOcean will give you $200 in credits for 2 months of use. You'll have to give them a form of payment. Don't worry! You won't get charged, as long as you remember to shut down any services you launch today.
• In the DigitalOcean UI, create your own Roman Python project.
  • Navigate to Projects / New Project. Name your project Roman Python and click Create Project.
  • In the Move Resources dialog, click Skip for now.
• Create your Roman Python app. Click Create App.
  • At the prompt, Create Resource from Source Code / Service Provider, select GitHub.
  • For Repository, login to your GitHub account and select your Roman Python repo.
  • Notice that Autodeploy is checked.
    • 🤔 What do you think Autodeploy does?
  • Click Next.
• On the Edit Plan page, select these options:
  • Plan: Basic
  • Size: $5/mo - Basic
  • Click the Back button.
  • Click Next.
• On the Environment Variables page, just take a look. Click Next.
  • 🤔 What might you use environment variables for?
• On the Info page, select App Info to edit more project details.
  • Edit your app name. Rename it roman-python.
  • Choose your Roman Python project
  • Click Save, then Next.
• On the Review page, take a look the settings. Click Create Resource.
• Go to Build Logs and watch your app build.
• Your app is now running in a production environment. To run your app's web UI, click the Live App button.

Continuous delivery

One way we reduce risk is by reducing batch size: our CD pipeline automatically rebuilds and redeploys every time we introduce a code change. Remember that Autodeploy setting? We left it turned on. Whenever we push new code to the repository, our CD pipeline will notice, clone the repository, build it, and deploy it.

• 🤔 Try it: change some code on your machine, run the tests to make sure everything is "green", and commit and push to git.
• 🤔 What did you change?
• 🤔 Exactly what happened when you pushed to git?
• 🤔 What are the risks of automatic deployment?

Safety: Add tests to your build pipeline

Another way we reduce risk is via test-driven development. We have a test suite that we run on our machine while writing code. We can enhance the safety of our deployments by also running these tests in the build & deploy environment.

• In App Settings / Components, select your roman-python app.
• In Commands, click Edit.
• Add a Build Command to run your tests: python app/test/tests.py. Click Save.
• Notice that when we change our app's configuration, the CD pipeline rebuilds it. Go to Build Logs and watch the new build. Notice that the pipeline now runs tests, and that all the tests passed.

Safety: blue/green deployments

• On your machine, intentionally introduce a test that fails. Commit and push your code to the repository.
• 🤔 What happens in the CD pipeline?
• On your machine, make that test pass . Commit and push your code to the repository.
• 🤔 What happens in the CD pipeline?