Modern OpenJDK comes with a built-in HTTP server, and you can also embed a relational database like H2 or of course SQLite. You can use it from many different languages, of course. Actually it sounds from the article like Kotlin or Java would have been a better fit than Rust for what they were doing. There are also things like Postgrest which turns postgres tables into REST APIs automatically.
But here's something to really chew on. Do we need the HTTP server at all?
Consider: why exactly do we need so much middleware plumbing for ordinary database driven web apps? A lot of this is to do with a winding evolutionary path rather than what you'd design with a clean slate.
Something I've been experimenting with lately is writing apps that connect directly to an RDBMS using its native protocol, over the internet, from a desktop app. Obvs the next step after is to try the same with a mobile app. Historically we've relied on web browsers and written translation layers for a few different reasons, but tech has been improving over time and some of those reasons are becoming obsolete:
1. Free relational databases were really rough back then and the commercial DBs often had weird limitations around distributing DB drivers. These days it's easier and postgres is a lot better.
2. You needed to slather lots of caches and other stuff in front of the RDBMS if you had high traffic. Modern DBs are a lot better at materialized views, cached query plans, read replicas etc. Postgres has a variety of load balancers that can sit in front of it and work around its per-connection overhead.
3. Security wasn't good enough. Nowadays you have features like row level security, security-definer views etc in the free DBs.
4. People translate everything to HTML/HTTP partly because it was too hard to distribute and update apps to Windows desktops/laptops in the 2000s, due to MS just generally losing the ability to execute and being distracted by stuff like Longhorn/WinFS. Browsers solved the basics of caching and refreshing of code for you. Now there's https://conveyor.hydraulic.dev/ which makes distributing desktop apps way easier. It's a lot more feasible now to just knock out a quick desktop app and upload to an S3 bucket, with built in online updates. Also the next release will support force-update-on-start, so you can get a web like experience where the user is always up to date so the schemas and client can be evolved in parallel.
If you could just write your UI using a 'real' UI toolkit and invoke directly to the DB from the UI code, you wouldn't need a lot of the microservices plumbing anymore, you wouldn't need to serialize stuff to JSON or HTML. You could just use the underlying DB protocol as an RPC layer and let the DB enforce business logic. It can be done for common kinds of enterprise apps today: there are only a few problems to solve, none of them especially hard. For instance a little service that turned OAuth SSO into client side certificates would make it easy to connect to a DB without needing to manage usernames or passwords. A tunnelling solution to get through awkward firewalls would also be useful (websockets etc).
For consumer apps there's more complexity. You wouldn't try to implement twitter that way for instance. But still, for the kind of SaaS-y thing that the article is about it could have saved a lot of complexity and improved iteration speed.