Backend Engineer - Ad Serving & Integrations

Job description

title: "Backend Engineer — Ad Serving & Integrations" subtitle: "Rust · Distributed Systems · Ad-tech" - Backend Engineer — Ad Serving & Integrations -Context & Vision In 2026, writing code is no longer the primary bottleneck; managing its complexity and ensuring its reliability is. We are building a highly resilient advertising platform with a very lean, senior internal team, and we intend to keep it that way. To achieve scale without the overhead of a large engineering department, we rely on an AI-first development paradigm and a philosophy borrowed from the best large-scale open-source projects. Our code is not public, but our governance is theirs: asynchronous communication, exhaustive written documentation, explicit rules, and uncompromising quality gates. It is the only way a small team of humans and AI agents ships serious systems without accumulating technical debt. This role owns the part of that platform where money and latency meet: the serving path and the integrations to external ad systems. -The Role You will own, end to end, the connectors and serving logic that turn an ad request into a served, billed impression. This is hands-on, systems-level backend work with a direct revenue impact and a low tolerance for error. 1. Ad Serving & Integrations. Build and own the integrations to external ad servers and demand partners, the serving gateway, and the augmentation and bidding logic that sits between them. You are the person who understands, precisely, how these systems talk to each other and why. 2. Correctness on the Hot Path. The serving path is real-time and handles money. You will hold the line on latency, on monetary correctness, on idempotency, and on the reconciliation between what was decided, what was cleared, and what was billed. A silent error here is a production incident. 3. AI-First Delivery.We expect AI to write the majority of the code; you are the editor, not the typist. You will specify work as explicit, self-sufficient issues, direct agentic tooling (e.g. Claude Code) to implement, and remain the final gatekeeper on every diff, whether it came from an agent or a human. 4. Governance & Documentation. Everything is written down. You will maintain Architecture Decision Records for the integration contracts you own, keep API definitions as the single source of truth, and enforce strict review on your own domain. If it is not documented, it does not exist. The Tech Stack - Language: Rust (backend, asynchronous services). - Interfaces: gRPC and REST service APIs, contract-first. - Data & Messaging:relational databases, event streaming. - Domain:ad serving, retail media, real-time bidding, auctions and reconciliation. - Cloud:Google Cloud Platform, Kubernetes. Profile & Requirements We are looking for a highly autonomous, systems-oriented backend engineer who is energised by a lean, high-quality environment and owns their surface completely. This role is not suited to someone who wants tickets handed to them inside a large team. Essential Experience - 5+ years building backend systems in production, with real ownership of availability, latency and correctness under load. - Rust in production or a serious open-source project — or exceptional depth in another compiled systems language (Go, C++) with a demonstrated, immediate willingness to master Rust. - Hands-on experience with asynchronous services, service-to-service APIs, and message streaming . - Ad-tech domain experience (ad servers, DSP/SSP, real-time bidding, retail media) is a strong advantage; the ability to reason about money, auctions and reconciliation is expected. -Core Competencies & Mindset - AI Development Lifecycle: genuine proficiency editing and validating AI-produced code, and turning ambiguous goals into ultra-clear specifications an agent can execute without a meeting. - Uncompromising Quality:a maniacal focus on the non-functional requirements — performance, security, reliability, correctness. You are the last line before production. - Distributed & complex systems: knowledge of, and a taste for, distributed and complex systems is very welcome. Tell us about the ones you have built or operated — what made them hard, and what you took from them. - Written & Asynchronous: exceptional written communication. You operate effectively in a globally distributed, async environment (Paris timezone +/- 3h). - Ownership: you treat the domain you own as yours, documentation included, and you do not wait to be asked.