The Same App, Built Twice
DevMentors shipped Trill as nine microservice repos, then rebuilt the identical product as a modular monolith three months later - giving us a controlled experiment in architecture that almost never exists in public.
Series
Trill Two Ways
In reading order.
- 13 parts
- ≈ 88 min total
- 13 published
Boundaries the Compiler Enforces
Trill's monolith makes every module type internal and gives each one an explicit friend list, so a cross-module reach is not a code-review conversation - it is a build error.
One Database, Eleven String Literals
Four physical Mongo databases collapse into one when Trill is rebuilt as a monolith - and the only thing keeping the modules apart afterwards is a private const string copied into eleven files.
A Framework Instead of Twenty-Four Packages
Trill's saga microservice references twenty-four third-party packages; the same saga as a module references one - because the monolith deleted Convey and rewrote 4,600 lines of it by hand.
AddX, UseX, and Two Deliberate Violations
Trill's hand-rolled framework follows the ASP.NET Core registration convention with unusual discipline, then breaks it twice on purpose - and the exceptions turn out to be more instructive than the rule.
Guid.Empty Is a Mode Flag
Trill's monolith puts the envelope fields on the message itself, then uses one sentinel value to mean this-is-a-synchronous-call in three unrelated subsystems that never mention each other.
The Contract Checker They Built After the Drift
The Trill monolith ships a startup-time validator that compares independently declared copies of the same message and crashes the app on a mismatch - the most original idea in either build, adopted by four declarations out of twenty-two.
Every In-Process Call Pays for MessagePack
Two lines in Trill's module client serialise and immediately deserialise every cross-module message, buying a future network hop at the cost of a round trip that never leaves the heap - and there is a benchmark project defending the choice.
Minimal APIs, Written by Hand
Trill's monolith implements typed Get, Post, Put and Delete extensions over IEndpointRouteBuilder on .NET 5 - the framework .NET shipped eighteen months later, complete with query binding by string replacement.
Eighteen Containers Become Two
Running Trill as microservices takes eighteen containers and twenty-two published ports; running the same product as a monolith takes mongo, redis and dotnet run - and only the monolith still starts from a clean clone.
In-Process Is Not Synchronous
Trill's monolith routes every cross-module event through an unbounded channel drained by one background service - so its flagship end-to-end test has to sleep for two seconds to observe the architecture working.
The Rewrite Kept Every Bug
Four non-trivial defects appear at near-identical line numbers in both builds of the same product - a ground-up rewrite by the same authors relocated them rather than finding any.
Ten Hours and No Way Back
The rewrite multiplied the JWT lifetime by ten and deleted the only way to revoke a token early - one change in a JSON file, the other an absent folder, and neither visible in any diff of the domain.