Explain what caching means inside GitLab and how it works.

Caching in GitLab is used to store intermediate data between builds (pipelines) to speed up repeated runs and reduce system load. For example, if a project has dependencies that are downloaded or built, they can be stored in the cache so that they are not downloaded or built again during the next run.

It works as follows: in the .gitlab-ci.yml file, you can define a cache key and paths to files or folders that need to be saved. When a job runs, GitLab checks if a suitable cache exists, and if so, restores it. After the job completes, the cache is updated if there were any changes.

Example of cache configuration:

cache:
  key: ${CI_COMMIT_REF_SLUG}
  paths:
    - node_modules/

Here, the cache saves the node_modules folder for each branch separately, which speeds up dependency installation.