Deploy multiple apps to Heroku from one Repository

.gitlab-ci.yml

stages:
  - deploy

deploy:frontend:
  script:
    - git remote add heroku-frontend https://heroku:[email protected]/frontend-app.git
    - git push --force heroku-frontend `git subtree split --prefix frontend-folder HEAD`:master
  only:
    - master
  stage: deploy

deploy:api:
  script:
    - git remote add heroku-api https://heroku:[email protected]/backend-app.git
    - git push --force heroku-api `git subtree split --prefix backend-folder HEAD`:master
  only:
    - master
  stage: deploy