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Comment by keyle | Hacker News Reader

Could someone TLDR me what Hexagonal architecture means?

    Hexagonal architecture brings order to chaos and flexibility to fragile programs by making it easy to create modular applications where connections to the outside world always adhere to the most important API of all: your business domain.

okay.

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Domain driven design with more hexagons and less Martin Fowler

Well here's the take from the Author itself: https://alistair.cockburn.us/hexagonal-architecture/

That’s a mighty lot of words, to say “functional core, imperative shell”.

Maybe I’m being glib, but damn, a whole article, and boatloads of fancy new terminology, just to re-state what the author succinctly landed on in the _first_ paragraph:

> Create your application to work without either a UI or a database so you can <do a bunch of nice stuff and make your life easier>”.

Indeed. And some great HN discussions of a great article to get inspired on the pattern:

- https://news.ycombinator.com/item?id=18043058 (Sep 2018, 127 comments)

- https://news.ycombinator.com/item?id=34860164 (Feb 2023, 39 comments)

I love a good rabbit hole, thank you!

I'm always surprised that this style of architecture isn't discussed in terms of functional purity [1].

To me, a hexagonal architecture essentially means creating an abstraction at the point between pure and impure functions.

The realization of this approach essentially means the core of your application should be entirely pure and as large as possible. And your impure adapters, at the application boundary, (e.g. a rest api, db client, file system, system clock, etc.) should be as small as possible and impure.

Doing this well essentially allows you to get the best of both worlds - highly coupled code (i.e.your pure functionality) and highly decoupled code (i.e. your pure-to-impure functionality).

Another good reason for leveraging "functional design" as an argument is that many of those skeptical of architectural patterns are ironically heavily onboard the "functional design" bandwagon. So it is a strong argument in a political sense also.

[1] https://en.wikipedia.org/wiki/Pure_function

Yes after 25 years this is how I see it. Isolate state into its little dirty corner, think in terms of data structure and its transformation. This has kept me sane for decades. It's simple but so many devs just haven't seen the light yet.

https://youtu.be/JubdZIdLQ4M?si=GkZ3tomeqIYzYyPk

Best explanation by far, worth the 5min watch

Step one: ignore the prefix, this has nothing to do with hex/six. And "ogon" meaning sides or struggle. The sides represent interfaces.

This arch really means use interfaces based on business use cases / domains. Call the User service/module and pass user ids into a billing service/module. Each service is over a defined interface (adaptor) that allows separation of concerns and separate data stores. You could use an in-memory port of the billing service and a real db for the user service service because both implementations leverage the same adapter code

No explicit dependencies in the core business domain, everything coordinates via interfaces defined by the needs of the core.

That's pretty much it. Everything else flows from there.

Pretty much nothing.

The bullshit remover condenses that down to the following:

> Bullshit.

Another similar/related idea to Google is the “onion architecture”.

(Because the diagram gives a better TLDR than than the hexagonal equivalent diagram, IMO)

yeah thanks I kept looking for a reason for the 6-way or 6-layers or something.

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