如何让我的rails资产由cloudflare而不是我的服务器提供？

I'm running a rails app on heroku and recently switched to cloudflare for CDN for asset serving. My understanding was that once I use cloudflare, my assets (ie js,css,images) would be served from cloudflare and not from my own server but in my heroku logs I still see the requests for assets. Do I need to configure something in my rails app like setting the asset_host or something? Thanks.I'm running a rails app on heroku and recently