assets_live_compile
Compile and save assets on demand instead of using rake assets:compile
This works just like rake assets:precompile but is triggered on the asset HTTP request, so the cost of compilation is due to the first asset request. Next time Nginx will find the static asset on public/assets.
Compile your assets by doing a warm up request :)
Configuration
config.assets.serve_static_assets = true
config.assets.compile = true
config.assets.cache_store = :assets_live_compile_store