Deploy from Gitlab CI to Dokku

.gitlab_ci.yml

variables:
    DOKKU_HOST: 'dokku.host.es'
    IP_DOKKU_HOST: '1.2.3.4'
    SSH_DOKKU_PORT: '22'
    PROJECT_NAME: 'project_name'
    
stages:
  - deploy_to_dokku

deploy_dokku:
  stage: deploy_to_dokku
  script:
   - mkdir -p ~/.ssh
   - echo "$SSH_PRIVATE_KEY" | tr -d '\r' > ~/.ssh/id_rsa
   - chmod 600 ~/.ssh/id_rsa
   - echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config
   - echo -e "Host $DOKKU_HOST\n  Hostname $IP_DOKKU_HOST\n  Port $SSH_DOKKU_PORT\n" >> ~/.ssh/config
   - ssh-keyscan -H $DOKKU_HOST >> ~/.ssh/known_hosts
   - git push dokku@$DOKKU_HOST:$PROJECT_NAME master
  when: manual
  only:
    - master