Sending Files Directly From Client to Amazon S3 — Signed URLs

Normally, when you upload a file from a client, the file gets sent to the application server, which then passes it on to S3.

// Normal upload flow:
File -> Client (Web Browser) -> Application Backend Server -> S3 

However, what if your server can’t handle the influx of files coming in? What if your server doesn’t have enough storage, memory, or CPU cycles? Then you can ask yourself — does my server do anything with this file, other than upload it to S3?