title: Sequelize Sync vs Migrations
body: <p>Im learning Sequelize and I'd like some clarification around syncing vs migrations.</p>
  
  <p>I understand that sync will create missing tables based on my model schema but I have also read that sync is meant for initializing the database whereas migrations are meant for production.</p>
  
  <p>If that is the case, the express-example shows <a href="https://github.com/sequelize/express-example/blob/master/bin/www#L23" rel="noreferrer">calling sync from <code>bin/www</code></a>. Is that something that should not be used in production?</p>
  
  <p>As an extension of this, if I am not to use sync in production, how do you apply model associations? Do I need to add them to migrations manually?</p>
  
  <p>Essentially I am asking for an explanation of how these two concepts are meant to work together.</p>
  
  <p>Thanks</p>