Using Git in Continuous Integration/Continuous Deployment (CI/CD)

From indie film enthusiasts to blockbuster bigwigs, the best teams in movie-making all have one thing in common: a system that allows them to work seamlessly together. In software development, the equivalent of such a system is a good Continuous Integration/Continuous Deployment (CI/CD) pipeline.

As the director leading the show behind the scenes, the CI/CD pipeline ensures that coding changes and adjustments from each of your development team (think writers, Cinematographers, editors, etc.) are orchestrated into a coherent, working application (a cinematic masterpiece!). But to properly manage this pipeline, one needs a reliable assistant, and this assistant is Git.

In setting this stage, this chapter throws spotlight on using Git in CI/CD, taking you through the fundamentals, simulation of scenarios with snippets of scripts prepped up for the code-sharing platform GitHub, and the ultimate presentation of your 'movie.'

Just as action sequences are core to a good thriller movie, version control is a key component of CI/CD. It lets developers simultaneously work on different parts of a 'script', branches, without interrupting others' work. Here, Git shines as a Distributed Version Control System (DVCS) - everyone has their local copy of the entire project's history. When changes are finalized, they can be pushed up to the main 'script' handled by the client.

# Clone a repository to your local system
$ git clone https://github.com/user/repo.git

A script, or in our case, code snippet, can undergo several takes or edits before a final version is agreed upon. It is broken into various scenes, or branches. Git branches are quick and easy to create and delete. Typically, you create a branch for each new feature or bug fix.

# Create a new branch 'new-scene'
$ git checkout -b new-scene  

After the scripts are set, and scenes filmed (read: the feature is coded), they need to be reviewed. This is where Git's "pull request" feature comes in handy. Pull requests display your proposed changes to teammates for review. You can show them the scenes filmed and review it before adding it into the final cut (your main branch).

# Push the branch to GitHub
$ git push origin new-scene

Once the branch has been pushed, you can open a pull request on GitHub, inviting your team for review. Post the review; if the changes pass, you can merge your branch with the main branch.

Now with scripts reviewed and final cuts ready, it's time for the actual filming or integration, which is the cornerstone of CI. Continuous Integration focuses on integrating work from all developers onto a shared main line several times a day.

CI looks for any 'bloopers' that can occur if the scenes don't fit together well (code conflict). It is here that a CI server tests the merged branches continually, assuring that no conflict remains and everyone's code is in sync forming a complete story (working application).

This code represents a simple Git flow integrated into a CI pipeline.

# .gitlab-ci.yml

stages:
  - build
  - test

build:
  stage: build
  script:
    - echo "Building the app"
    - (build script here)

test:
  stage: test
  depends_on:
    - build
  script:
    - echo "Testing the app"
    - (test script here)

The CI server (like Jenkins, Travis, or GitLab CI/CD) recognizes when a commit has been made and pushed to the repository. It then pulls these changes and starts building the application and running tests.

As the name implies, Continuous Deployment is the second half of the CI/CD process and directly follows a successful integration. In our movie-making example, deployment represents the release of the movie into theaters or television. It specifically involves automated deployments of merged and tested branches to a staging or production environment.

# .gitlab-ci.yml

deploy_production:
  stage: deploy
  script:
    - echo "Deploying to production server"
    - (deployment script here)
  only:
    - master  # deploy only when the master branch changes

The 'master' branch is typically the production-ready branch that gets deployed. The 'only' keyword here signifies that this job should only run when the 'master' branch changes. This ensures your deployment only contains reviewed and approved scenes.

In conclusion, Git provides the necessary tools to manage and maintain a proper CI/CD pipeline, fostering efficient teamwork and coding practices. Understanding and using Git in a CI/CD pipeline is like having your Production Supervisor, ensuring all scenes intertwine seamlessly into a successful blockbuster.