Everything was controlled by a single Postgres database that made very heavy use of stored procedures, that called other procedures, that called others. It was one giant program inside the database. It took me a while to comprehend what he'd done but it was really great. The database ran everything and all those functions made sure that audit logs were kept, that the calls were allowed for the user ID being passed in, and some of these procedures made external calls to APIs including getting things like SSL certificates.
It was a magnificent monolith inside a database.
I worked on the periphery of the database (it was truly Lee's domain) and he'd tell me what output to expect or API to create and I'd code to his spec. and we'd just hook it up.
If any single artefact represents what he did at Cloudflare, it's that database. And he used to code it on a laptop we called "The Beast" because it was so crazily heavy and overloaded with memory etc. that he'd carry around a mini, test Cloudflare wherever he went.