// Learning · 04
How a whole system is cut up, and why.
Stack the code by job: presentation on top, data at the bottom.
Business rules in the middle; frameworks and databases plug in.
One deployable, split inside into modules that keep their distance.
Small services, each owning its data, deployed on their own.
Announce what happened; whoever cares reacts. Nobody waits.
Split writing from reading so each side can scale on its own.
Store the events, not the state; replay them to get the state.
Write the function; the cloud runs, scales and bills it per use.
A boundary inside which every term means exactly one thing.
Grow the new system around the old one until the old one is gone.