Role Purpose

Modern Milkman is rebuilding the backbone of its technology platform. We’re moving core business logic, order management, and operational workflows from a legacy C# microservices architecture into a new Rust-based modular monolith; faster, safer, and far more maintainable.

This role exists to both bridge and build. You’ll own critical migrations from .NET into Rust while simultaneously developing new features and integrations that expand the capabilities of our next-generation system. Your work will directly shape how millions of deliveries, returns, and memberships run every week across the UK and US.

Technology Landscape

Our new platform is a fully modular Rust monolith, built with Actix-Web, leveraging Rust’s performance and safety guarantees. We avoid heavy ORMs in favour of explicit SQL and type-safe data handling. Everything is thoroughly tested, built for resilience and correctness from the ground up.

The legacy world runs on C#/.NET, delivering value but increasingly out of alignment with our engineering standards. It remains critical to daily operations and will continue to coexist for some time, requiring thoughtful integration and migration.

We use PostgreSQL for new systems (with some remaining MS SQL Server workloads), Datadog for observability, and AWS as our primary cloud platform.

Performance Expectations

Success in this role will be measured by clear, operational outcomes rather than activity:

● Service quality: measurable improvements in availability, latency, and error rates across customer and operations journeys. ● Migration delivery: completion of defined C#-to-Rust migrations with no functional regression and clear performance gains. ● Engineering standards: creation and ongoing maintenance of clear, documented standards for Rust development, testing, and observability.

● Team discipline: fostering a culture of diligence, code quality, and operational accountability within the Customer Team and beyond.

● You’ll be expected to balance shipping features with raising the bar; ensuring every line of code contributes to stability, clarity, and long-term maintainability.

Key Responsibilities

● Design, build, and maintain performant Rust services within our modular monolith, using Actix-Web and explicit SQL.

● Migrate critical business logic from legacy C# systems into Rust, ensuring accuracy, performance, and observability.

● Identify, prioritise, and deliver improvements to reliability, latency, and error rates across customer and operations workflows.

● Maintain disciplined testing, code review, and documentation practices that set the standard for the wider team.

● Define and uphold engineering conventions; including module structure, observability, and deployment patterns, and ensure they are explained and adopted consistently.

● Collaborate with other teams (Product, Operations, Data) to translate domain problems into robust technical solutions.

● Support architecture and platform evolution, contributing to design discussions and long-term technical decisions.

● Participate in incident reviews and post-mortems, ensuring lessons are codified into future development.

● Offer technical guidance to peers when needed, by example rather than title.

What you'll bring

● You’re a senior engineer who prefers clarity over ceremony. You care about correctness, reliability, and the integrity of the systems you build. You can explain technical reasoning clearly to both engineers and non-technical peers, and you don’t lose patience when the details matter.

● You’re deeply experienced in Rust, comfortable designing large, modular systems and reasoning about concurrency, performance, and correctness. You may not be a C# expert, but you’re pragmatic enough to dive into it, extract what’s valuable, and migrate it cleanly into Rust when needed.

● You balance speed with precision, document as you go, and leave systems cleaner than you found them. You’re comfortable owning a problem end-to-end; from design and data model to deployment and monitoring. You like Rust because it enforces discipline, and you value that same discipline in your teams.

● If you see a broken abstraction, you fix it. If you see a messy process, you streamline it. You understand that the product and the system succeed together, not in isolation.