What are protected branches and protected variables in GitLab CI?

Protected branches and protected variables are security features that control who can push to critical branches and which jobs can access sensitive CI/CD variables.

# Protected variables are set in:
# Settings > CI/CD > Variables > Add variable
# Tick "Protected variable" checkbox

# A protected variable is ONLY available in jobs running on:
# 1. Protected branches (e.g. main, production)
# 2. Protected tags

# Example: PROD_API_KEY is protected:
deploy-production:
  stage: deploy
  script:
    - echo "Using: $PROD_API_KEY"    # only available because main is protected
  rules:
    - if: $CI_COMMIT_BRANCH == "main"  # main is a protected branch

# feature branches (unprotected) CANNOT access $PROD_API_KEY:
test-on-feature:
  script:
    - echo "$PROD_API_KEY"   # will be empty - variable not available here
  rules:
    - if: $CI_COMMIT_BRANCH =~ /^feature/

# Protected branches in GitLab:
# Settings > Repository > Protected branches
# Can restrict push access to Maintainers, Developers, No one
# Can require merge request approval before merging
# Can require status checks (pipeline must pass)

Security design: this combination means developers on feature branches cannot access production secrets even if they have access to the project. Only pipelines running on protected branches (typically main or release tags) can use protected variables like production API keys.

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