gitlab CI/CD notes

1.What is a pipeline?

A pipeline is a series of connected steps, similar to an assembly line in a car factory, where each step must be done in a specific order to build a final product. In a pipeline:

• Each step’s output becomes the next step’s input.
• Some steps, like adding wheels, can be done in parallel.
• Numerous steps are required, from initial assembly to final testing, to ensure quality before delivering to the customer.

2.GitLab’s architecture:

• A GitLab Server provides the interface and stores repositories but delegates job execution to GitLab Runners.
• This separation allows GitLab to scale efficiently, as the server doesn’t run jobs directly.
• Runners, found under Settings > CI/CD > Runners in each project, execute pipeline jobs. GitLab.com offers Shared Runners, but users can also set up custom Runners on their infrastructure and assign them to specific projects for more tailored control.

3.Why GitLab/GitLab CI?

GitLab is a modern tool positioned to become a market leader. It offers:

• A scalable, modern architecture
• Easy integration with Docker
• Pipeline-as-code capabilities
• A partially open-source model

4.What is CI/CD?

• CI (Continuous Integration): A development practice where code changes are frequently integrated with the work of other developers. CI includes:

  • Verifying builds and running unit tests
  • Ensuring adherence to coding guidelines
  • Integrating code multiple times per day
  • Producing a deployable package

• CD (Continuous Delivery): Follows CI and focuses on testing the package created by CI to prepare it for production:

  • Tests the installability and compatibility of the package in a production-like environment
  • Requires manual approval before deploying to production

• CD (Continuous Deployment): Extends Continuous Delivery by automatically deploying every tested package to production without manual intervention, provided it passes all previous stages.

5.Advantages of CI:

• Detects errors early in development
• Reduces integration issues
• Enables faster development pace

6.Advantages of CD:

• Ensures every change is ready for release
• Lowers deployment risk
• Speeds up value delivery with more frequent releases

7.What is Docker?

Docker is a virtualization tool that uses images—pre-configured software environments with all necessary dependencies.

• Images: Files with instructions to package code, tools, and dependencies.
• Containers: Executed images, functioning similarly to virtual machines but are lighter.

In traditional CI servers, dependencies are installed directly on the server. However, GitLab CI utilizes Docker images for dependency management, allowing GitLab CI Runners to use specified images, simplifying and scaling the setup.

8.Why Do Jobs Fail?

Jobs fail due to command exit codes:

• 0: Command executed successfully
• >0: Command failed

9.Cache vs Artifacts

Though similar, caches and artifacts serve different purposes in CI/CD:

• Artifacts:

  • Outputs from the build process (e.g., deployable packages).
  • Can be partial outputs if built across stages.
  • Used to pass data between jobs or stages.

• Cache:

  • Temporary storage for project dependencies.
  • Not intended for storing artifacts, even if possible.

For more details, refer to GitLab documentation.