Amazon S3 launched in 2006. By 2013 it held two trillion objects; by 2021, over a hundred trillion.

It is the substrate under a remarkable amount of this series — routing tiles, video segments, email attachments, Kafka’s tiered storage. Every time an earlier design said “put it in object storage and forget about it,” this is what it was leaning on.

So the interesting question is: how do you promise eleven nines of durability on hardware that fails constantly?

A message queue sits between two services so they don’t have to know about each other. The producer writes and moves on; the consumer reads when it’s ready. Neither has to be up when the other is.

That buys you four things: decoupling, independent scaling of each side, availability when one side is down, and asynchronous communication so nobody blocks.

Simple enough to describe in a sentence. The design is not simple at all, and the reason is that we’re going to build the harder version: not just a queue that hands messages over and forgets them, but one that retains everything for two weeks and lets consumers read it again from any point.