rswag - best practice for adding servers

I'm currently trying to dynamically add server URL's to my swagger documentation. I have the following code:

# spec/swagger_helper.rb
servers: [
{
    url: 'https://{defaultHost}',
    variables: {
      defaultHost: {
        default: Rails.application.credentials.hostname
      }
    }
  }
]

To ensure that swagger gets generated for every heroku environment I have added a release command in my Procfile:

release: bundle exec rake rswag

I am still getting defaultHost as localhost:3000 in the heroku instance of the API documentation.

I think that Heroku doesn't let you generate the swagger.yml on production. You have to run the rake rswag locally and then push that change to Heroku.