Originally published at blog.whynext.app.
It started as an ordinary cleanup problem. Users upload media files (recordings and images) through presigned URLs. The server issues an upload URL, the client uploads straight to S3, then calls a commit API to say "register this key as a real asset." The problem is what happens when someone gets a presign but never commits. The app crashes, the network drops, the user leaves the screen, and the bucket is left with an object that isn't registered anywhere.
I wanted a lifecycle rule to clean these up, but there was no way to write one. Committed and uncommitted objects were mixed under the same prefix, so any rule that says "delete old things" would delete real assets too. A daily upload quota kept the pile from growing fast, but the fact remained: there was no path to reclaim the space.
The design: what isn't committed lives in tmp
The backbone of the fix is key namespace separation.
