And, reading between the lines o/t article: stable interfaces. The more stuff exists that uses an interface, the slower it tends to evolve. So very-popular interfaces tend to be stable & long-lived by necessity, because 'breaking the world' is not an option.

Come to think of it: that also applies to physical infrastructure: building codes & materials, road networks, AC power grids, gas stations + associated infrastructure to supply those, telecom networks, etc etc. Anything deployed at scale tends to evolve slowly.

Come to think of it: ... [biology]

If I’ve understood then, a narrow waist architecture follows two principles:

- code to an interface not an implementation

- segregate interfaces, don’t overload them with responsibilities

That’s not really an architecture though, it’s just basic principles of modularization.

True, which is perhaps why it's unclear what the difference is between a "skinny waist" and hexagonal architecture, "ports and adapters".

hexagonal architecture gives you the direction of the "waist", not its thickness.

You could have a really skinny interface (one method call only):

    class TaxLogic {
        data = iDatabase.loadOneDatabaseRow(id);
        process(data);
    }

    interface IDatabase {
        loadOneDatabaseRow(id);
    }

    class PostgresDb implements IDatabase {
        loadOneDatabaseRow(id) {...}
    }

But this violates ports and adapters because the logic is on the outside and the database is on the inside.

This is just "loose coupling" expressed with different terminology.

It's not wrong but it's also nothing new - it's about as novel as object oriented programming or DRY.

>shitty overcomplicated interfaces for simple things.

This is tight coupling.

No tight coupling is a strong immutable dependency. That doesn't necessarily mean complexity. It could mean a leaky abstraction around a simple API, like half of POSIX etc.

What does screw you is things that are hard to reason about and you don't know if you can reason about them until many years have passed or you've tried to replace either side of the abstraction.