If you have an application server then you still have RPCs coming from your user interface, even if you run the whole DB in process. And indeed POSIX has nothing to say about this. Instead people tend to abuse HTTP as a pseudo-RPC mechanism because that's what the browser understands, it tends to be unblocked by firewalls etc.

One trend in OS research (what little exists) is the idea of the database OS. Taking that as an inspiration I think there's a better way to structure things to get that same simplicity and in fact even more, but without many of the downsides. I'm planning to write about it more at some point on my company blog (https://hydraulic.software/blog.html) but here's a quick summary. See what you think.

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In a traditional 3-tier CRUD web app you have the RDBMS, then stateless web servers, then JavaScript and HTML in the browser running a pseudo-stateless app. Because browsers don't understand load balancing you probably also have an LB in there so you can scale and upgrade the web server layer without user-visible downtime. The JS/HTML speaks an app specific ad-hoc RPC protocol that represents RPCs as document fetches, and your web server (mostly) translates back and forth between this protocol and whatever protocol your RDBMS speaks layering access control on top (because the RDBMS doesn't know who is logged in).

This approach is standard and lets people use web browsers which have some advantages, but creates numerous problems. It's complex, expensive, limiting for the end user, every app requires large amounts of boilerplate glue code, and it's extremely error prone. XSS, XSRF and SQL injection are all bugs that are created by this choice of architecture.

These problems can be fixed by using "two tier architecture". In two tier architecture you have your RDBMS cluster directly exposed to end users, and users log in directly to their RDBMS account using an app. The app ships the full database driver and uses it to obtain RPC services. Ordinary CRUD/ACL logic can be done with common SQL features like views, stored procedures and row level security [1][2][3]. Any server-side code that isn't neatly expressible with SQL is implemented as RDBMS server plugins.

At a stroke this architecture solves the following problems:

1. SQL injection bugs disappear by design because the RDBMS enforces security, not a highly privileged web app. By implication you can happily give power users like business analysts direct SQL query access to do obscure/one-off things that might otherwise turn into abandoned backlog items.

2. XSS, XSRF and all the other escaping bugs go away, because you're not writing a web app anymore - data is pulled straight from the database's binary protocol into your UI toolkit's data structures. Buffer lengths are signalled OOB across the entire stack.

3. You don't need a hardware/DNS load balancer anymore because good DB drivers can do client-side load balancing.

4. You don't need to design ad-hoc JSON/REST protocols that e.g. frequently suck at pagination, because you can just invoke server-side procedures directly. The DB takes care of serialization, result streaming, type safety, access control, error reporting and more.

5. The protocol gives you batching for free, so if you have some server logic written in e.g. JavaScript, Python, Kotlin, Java etc then it can easily use query results as input or output and you can control latency costs. With some databases like PostgreSQL you get server push/notifications.

6. You can use whatever libraries and programming languages you want.

This architecture lacks popularity today because to make it viable you need a few things that weren't available until very recently (and a few useful things still aren't yet). At minimum:

1. You need a way to distribute and update GUI desktop apps that isn't incredibly painful, ideally one that works well with JVM apps because JDBC drivers tend to have lots of features. Enter my new company, stage left (yes! that's right! this whole comment is a giant ad for our product). Hydraulic Conveyor was launched in July and makes distributing and updating desktop apps as easy as with a web app [4].

2. You're more dependent on having a good RDBMS. PostgreSQL only got RLS recently and needs extra software to scale client connections well. MS SQL Server is better but some devs would feel "weird" buying a database (it's not that expensive though). Hosted DBs usually don't let you install arbitrary extensions.

3. You need solid UI toolkits with modern themes. JetBrains has ported the new Android UI toolkit to the desktop [5] allowing lots of code sharing. It's reactive and thus has a Kotlin language dependency. JavaFX is a more traditional OOP toolkit with CSS support, good business widgets and is accessible from more languages for those who prefer that; it also now has a modern GitHub-inspired SASS based style pack that looks great [6] (grab the sampler app here [7]). For Lispers there's a reactive layer over the top [8].

4. There's some smaller tools that would be useful e.g. for letting you log into your DB with OAuth, for ensuring DB traffic can get through proxies.

Downsides?

1. Migrating between DB vendors is maybe harder. Though, the moment you have >1 web server you have the problem of doing a 'live' migration anyway, so the issues aren't fundamentally different, it'd just take longer.

2. Users have install your app. That's not hard and in a managed IT environment the apps can be pushed out centrally. Developers often get hung up on this point but the success of the installed app model on mobile, popularity of Electron and the whole video game industry shows users don't actually care much, as long as they plan to use the app regularly.

3. To do mobile/tablet you'd want to ship the DB driver as part of your app. There might be oddities involved, though in theory JDBC drivers could run on Android and be compiled to native for iOS using GraalVM.

4. Skills, hiring, etc. You'd want more senior devs to trailblaze this first before asking juniors to learn it.

[1] https://www.postgresql.org/docs/current/ddl-rowsecurity.html

[2] https://docs.microsoft.com/en-us/sql/relational-databases/se...

[3] https://docs.oracle.com/database/121/TDPSG/GUID-72D524FF-5A8...

[4] https://hydraulic.software/

[5] https://www.jetbrains.com/lp/compose-mpp/

[6] https://github.com/mkpaz/atlantafx

[7] https://downloads.hydraulic.dev/atlantafx/sampler/download.h...

[8] https://github.com/cljfx/cljfx