So You Want to Modernise a Monolith? Try One Bite at a Time

Have you ever found yourself operating a system you aren’t familiar with? Maybe it was written in a really old framework. Maybe it was a language you don’t understand that came through an acquisition. Did you find yourself getting frustrated with slow delivery, integration test overload, duplicate entities, and architectural dead ends? You try everything to understand and improve these old systems, but eventually you realise it’s fruitless. You need to modernise! But where do you even start?

This is the situation we found ourselves in at Flipdish in 2023. We were operating with not one, but two monoliths - our original .NET (Framework!) system and a second JavaScript stack inherited through acquisition. This talk shares how we scaled modernisation from a single serverless pilot to a company-wide platform approach. We adopted AWS serverless, embraced event-driven architecture, and built a Golden Path with reusable templates, governance-as-code, and shared tooling to reduce friction. Datadog acted as a key platform partner throughout, giving us visibility across monoliths and our new Domain Services, tracking CI pipelines and cloud costs, and enabling a consistent view across fragmented systems. It helped align teams and accelerate change without sacrificing control.

You’ll hear what worked, what didn’t, and what we would approach differently if we started again. This isn’t a polished success story - it’s a practical account of how we’re moving from tightly coupled monoliths to independently owned, event-driven domain services. If you’re modernising a complex system or coordinating change across multiple teams, you’ll leave with clear, tested strategies for maintaining momentum, ensuring visibility, and enabling long-term architectural evolution - without disrupting day-to-day delivery.