I'm talking about "how do the files get into CF in the first place" rather than "how does my app serve them from CF once they are there"
so in the context of Rails and Heroku, how does the backend of my app know to send the files to Cloudfront, esp a file which might only rarely be requested? For example, a user's avatar which might only be shared if they ever log in again -- compared to a CSS file which may well be referenced on most every request
how did the images/css/assets get into Cloudflare in the first place? You set up the CDN, you tweak some settings for production and .... well, I can't tell.