A system that has run for over twenty years still underpins core production across dozens of sites worldwide.
It's now at end of life, and replacing it is a funded, multi-year programme.
You'd own the back-end architecture for the new one.
This is business-critical in the literal sense: when the current system goes down, production stops.
So the standards you set are load-bearing from week one, and the work shows up where the business actually feels it.
It's greenfield in the languages that matter (Kotlin, Spring Boot, PostgreSQL, an event-driven core).
The harder problem is the knowledge itself.
Two decades of hard-won operational logic sits in the heads of a few domain experts and inside a legacy database nobody wants to touch.
A large part of the job is building the migration that lifts that knowledge into a clean, event-driven codebase, one area at a time, without dropping a single transaction in a business that never pauses.
A few things that matter: You've led back-end architecture on Kotlin or Java, because the domain-driven and event-driven patterns the rest of the team builds on will be yours to set from the start.
You've run an incremental migration of a live system before, or the problem genuinely pulls at you, so keeping old and new in step without data loss is the part you're here for.
You're comfortable working with non-engineers, because the people who hold the domain knowledge aren't developers, and pairing with them is how it gets captured.
Remote, with roughly 1-2 days a month on-site in Scotland.
Outside IR35, 12+ month project.