Senior Backend Engineer (RUST) – Freelance

Context

Our client is a Parisian scale-up building a high-growth consumer social app, with a highly international team (68% non-French profiles). We're looking for a senior Backend freelancer to join the product team as a full contributor, with real technical ownership over critical components.

The Backend team handles both server-side development and the shared network/sync layer between iOS and Android (written in Rust). One team, both ends of the same data.

What you'll do

• Build systems designed for massive traffic and horizontal scalability

• Contribute to a shared Rust component for iOS/Android (networking, data sync, feature logic)

• Collaborate with iOS and Android engineers to maintain a unified cross-platform experience

• Join feature brainstorming and design sessions

• Own your scope: monitor analytics, manage incidents, drive bug fixes

Contract details

• Freelance – long-term mission

• On-site 5 days/week in Paris, near Opéra (Metro 3/8/9, RER A)

• Working language: English

What we're looking for

• Production experience with Rust, or strong background in C++, C, or OCaml

• Hands-on with distributed systems in prod (Kafka, Redpanda, ScyllaDB, Cassandra, or similar)

• Strong instincts about consumer social products — what makes them work, what makes them fail

• Autonomous, ownership-driven, feedback-oriented