On: How I write back ends

[vearwhershuh]

Great article in general, but this is absolute gold:

"Before you rush to embrace the microservices paradigm, I offer you the following rule of thumb: if two pieces of information are dependent on each other, they should belong to a single server. In other words, the natural boundaries for a service should be the natural boundaries of its data."

[fjp → vearwhershuh]

I'm curious what's a good rule of thumb for "dependent on each other". A foreign-key relationship? That's... pretty much everything unless you have two completely separate business lines.

[fpereiro → fjp]

This is not an easy question to answer, but in my experience it pays off to ponder it carefully.

So far, the heuristic that seems to work better for me is to keep the overall surface of the app small and try to keep everything in a single app. Lately, however, I'm convinced that extracting parts of the code as separate services (in particular, for handling users, logs, and statistics) would make the overall structure simpler. Dissecting this a little bit, an external user service is equivalent to middleware, whereas logs and statistics are write-only, after-the-fact side effects (from the perspective of the app), so bidirectional interaction with them is not needed for the purposes of serving a particular request. What I try to avoid is to have a server route that involves (necessarily) asynchronous logic between services to check the consistency of an operation.

In terms of "business logic", I feel that whatever lies within a transactional boundary should be in the same service; i.e., if two users share a resource, both the information of who owns the resource and who can access the resource should be in the same service. But I suspect there might be a lot more of thinking to be done in this regard.