Legacy modernization, without stopping the business.
Most legacy rebuilds fail for the same reason: a single architectural pattern gets applied everywhere because it's familiar, not because it fits. Feneco picks from a working range of patterns for the system in front of us, and migrates the data and the business under full production load — not a rewrite that quietly stalls for a year.
Patterns we choose from — not a single default
A CRUD-heavy internal tool doesn't need the same architecture as a system processing regulated financial transactions. The pattern is a decision, made per system:
Clean Architecture
Domain logic isolated from frameworks, databases and delivery mechanisms — for systems that need to outlive whatever's fashionable this year.
CQRS + DDD
Reads and writes modeled separately, aggregates and invariants enforced by the domain itself — for systems where the business rules are the hard part.
Vertical Slice Architecture
Each feature owns its full stack, end to end, instead of being spread across shared layers — for systems that need to add capability fast without a growing shared core.
REPR (Request-Endpoint-Response)
One focused endpoint per use case, no generic controllers doing five unrelated things — for APIs where clarity matters more than DRY-ing out every route.
Minimal APIs
Thin, fast, low-ceremony endpoints where a full MVC pipeline is more structure than the problem needs.
How the migration runs
Audit under real load
Map what the legacy system actually does — including the parts nobody documented — before deciding what changes. Single points of failure and bottlenecks get identified against real traffic, not assumptions.
Migrate data through domain rules, not scripts
A legacy database rarely has a clean schema to copy. Data moves through the same domain methods and invariants the new system enforces — dependency-ordered, reconciled, with a rehearsed rollback before cutover.
Ship without stopping the business
Zero-downtime rollouts, feature-by-feature where the pattern allows it (vertical slices help here), and a fallback path at every stage — modernization is a liability the moment it takes the business offline to deliver.
Proof
Feneco rebuilt Liren Language & Communications' ~1,500-file PHP legacy into a modular .NET monolith on CQRS and DDD, with a dependency-ordered data migration and a rehearsed rollback before cutover — now running training operations across Luxembourg, Belgium, France and the UAE. Before Feneco existed, its founding engineer led the same discipline at Commonwealth Bank, migrating the Buy Now Pay Later platform onto Clean Architecture on AWS under full production load.
When the modernization also means a new AWS footprint, see Cloud & AWS Architecture.
If a legacy system is the thing standing between your team and how the business actually needs to run, let's talk.