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Comment by kassner | Hacker News Reader

I feel the article could have ended after Step 1. It makes the point that you don’t have to follow REST and can build your own session-dependent API endpoints, and use them to fetch data from a component.

I don’t see a point in making that a server-side render. You are now coupling backend to frontend, and forcing the backend to do something that is not its job (assuming you don’t do SSR already).

One can argue that its useful if you would use the endpoint for ESI/SSI (I loved it in my Varnish days) but that’s only a sane option if you are doing server-side renders for everything. Mixing CSR and SSR is OK, but that’s a huge amount of extra complexity that you could avoid by just picking one, and generally adding SSRs is mostly for SEO-purposes, which session-dependent content is excluded anyway.

My brain much prefers the separation of concerns. Just give me a JSON API, and let the frontend take care of representation.

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The point of doing a server-side render follows from two other ideas:

* that the code which fetches data required for UI is much more efficiently executed on the server-side, especially when there's data dependencies - when a later bit of data needs to be fetched using keys loaded in a previous load

* that the code which fetches and assembles data for the UI necessarily has the same structure as the UI itself; it is already tied to the UI semantically. It's made up out of front end concerns, and it changes in lockstep with the front end. Logically, if it makes life easier / faster, responsibility may migrate between the client and server, since this back end logic is part of the UI.

The BFF thing is a place to put this on the server. It's specifically a back end service which is owned by the front end UI engineers. FWIW, it's also a pattern that you see a lot in Google. Back end services serve up RPC endpoints which are consumed by front end services (or other back end services). The front end service is a service that runs server-side, and assembles data from all the back end services so the client can render. And the front end service is owned by the front end team.

BFF is in practice a pain in the ass, it is large enterprise like Google's compromise but many ppl are trying to follow what Google does without Google's problem scope and well-developed infra.

Dan's post somehow reinforces the opinion that SSR frameworks are not full-stack, they can at most do some BFF jobs and you need an actual backend.

The alternative really is as Dan says: you end up with a bunch of REST endpoints that either serve up too much, or have configuration flags to control how much they serve, simply to satisfy front end concerns while avoiding adding round trip latency. You see this in much smaller apps than Google scale. It's a genuine tension.

Usually the endpoints get too fat, then there's a performance push to speed them up, then you start thinking about fat and thin versions. I've seen it happen repeatedly.

> The front end service is a service that runs server-side, and assembles data from all the back end services so the client can render. And the front end service is owned by the front end team.

Congratulations, you reinvented GraphQL. /s

Jokes apart, I don’t care much about the technology, but what exactly are we optimizing here? Does this BFF connect directly to the (relational/source of truth) DB to fetch the data with a massaged up query, or it just uses the REST API that the backend team provides? If the latter, we’re just shifting complexity around, and if the former, even if the it connects to a read-replica, you still have to coordinate schema upgrades (which is harder than coordinating a JSON endpoint).

Just let the session-dependent endpoint live in the backend. If data structure needs changes, backend team is in the best position to keep it up to date, and they can do it without waiting for the front end team to be ready to handle it on their BFF. A strong contract between both ends (ideally with an OpenAPI spec) goes a really long way.

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