AWS S3 HLD: Object Storage That Loses Nothing (Erasure Coding)

"Design S3." Object storage looks like a giant hash map — PUT key → bytes, GET key → bytes — and at the API it is. The depth is in one promise: eleven nines of durability. S3 is engineered to lose roughly one object in a hundred billion per year, across disks that fail constantly and whole datacenters that occasionally go dark. You cannot get there by hoping; you get there by spreading every object across independent failure domains and computing enough redundancy to rebuild whatever dies — at a storage cost you can actually afford. The keystone is erasure coding: instead of keeping three full…