What happens after GitLab downloads the code?

After downloading the code (cloning the repository), GitLab CI/CD runs a pipeline — a set of jobs and stages defined in the .gitlab-ci.yml file at the root of the repository.

Main stages of a typical pipeline after code download:

1. Stages: The pipeline is divided into stages that are executed sequentially. Tasks within the same stage can run in parallel.
2. Jobs: Each task runs on a separate Runner. A Runner is an agent that picks up jobs from GitLab CI/CD and executes them.
3. Commands: Inside each job, commands specified in the script section of .gitlab-ci.yml are executed. These commands may include:
   • Building the project (e.g., compiling code, packaging artifacts).
   • Running tests (unit tests, integration tests, etc.).
   • Checking code quality (linting, static analysis).
   • Creating Docker images.
   • Deploying to testing, staging, or production environments.
   • Other necessary actions.
4. Dependencies: Jobs can depend on the results of previous jobs using the needs keyword.
5. Artifacts: The results of jobs (e.g., compiled code, test reports, Docker images) can be saved as artifacts, which are available for download or used in subsequent jobs.
6. Caching: Dependencies or temporary files can be cached between job runs to speed up execution.
7. Reporting: The results of execution (success/failure), logs, and artifacts are accessible in the GitLab interface.

Sample .gitlab-ci.yml structure:

stages: # Define stages
  - build
  - test
  - deploy

build_job: # Define a job
  stage: build # Belongs to the build stage
  script: # Commands to execute
    - echo "Building the project..."
    - mvn package # Example build command for Maven
  artifacts: # Save artifacts
    paths:
      - target/*.jar

test_job:
  stage: test
  script:
    - echo "Running tests..."
    - mvn test # Example command to run tests
  needs: # Dependency on previous job
    - build_job

deploy_job:
  stage: deploy
  script:
    - echo "Deploying the application..."
    - docker build -t my-app . # Example Docker build
    - docker push my-app # Example pushing image to repository
  only: # Condition for job execution
    - main # Only on commits to the main branch

Thus, after code download, GitLab CI/CD orchestrates the execution of a user-defined workflow aimed at building, testing, and deploying the application.