A 100 MB upload through your API server holds a connection, memory, and a worker for the whole transfer. With a few users uploading at once, your app feels slow even though nothing is wrong with your code. The common fix is to let the browser send the file straight to cloud storage (S3, Cloudflare R2, and similar). The backend stops carrying the bytes and only decides who may upload what. This post covers the frontend side of that flow: browser APIs, a React implementation, progress, cance...