The .gitlab-ci.yml file is the configuration file that defines your GitLab CI/CD pipeline. By default GitLab looks for it in the root directory of the repository, and a project setting can point to a different path.
The file defines:
the pipeline structure: stages, jobs and scripts
when and how each job runs
deployment environments
variables, artifacts and dependencies between jobs
When you push code, GitLab reads this file and starts the pipeline it describes. Because it is YAML stored in the repository, the pipeline is version-controlled and easy to read.
Rewriting in plainer words…
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