backend engineer

At Flexcity, we help the European power system become smarter, more flexible and more sustainable by connecting industrial assets (batteries, e-boilers, heat pumps, data centers...) to energy markets. A subsidiary of Veolia Group, we combine scale-up agility with the stability of a global leader. At Flexcity, tech is a business driver, powering optimization and financial performance across Europe.

As a Senior Backend Developer F/H/X in the Strategy team, you will build the systems that optimize asset behavior and maximize €/MWh value through fully automated decision-making.

The team works at the intersection of backend engineering and data science, powering forecasting models, MILP optimizers, simulations and large-scale historical data pipelines. Your work directly improves financial outcomes for clients and Flexcity.

You will work end-to-end with a Product Manager and Engineering Manager in a high-autonomy feature team.

Your role focuses on:

• Backend Development (80%)

• Build backend services powering optimization, forecasting and decision engines.

• Design scalable pipelines handling large datasets and computational workloads.

• Own features from design to production monitoring.

• Team & Engineering Improvement (10%)

• Improve engineering standards, workflows and technical quality.

• Contribute to a strong culture of craftsmanship and continuous improvement.

• Technical Leadership (10%)

• Partner with Product Managers on feasibility, scope and trade-offs.

• Ensure architectural consistency and long-term system quality., We use a modern, well-crafted tech stack that emphasizes clean architecture, reliability and developer excellence.

• Languages: Kotlin + SpringBoot, Go, Python
• Hexagonal architecture / Domain-Driven Design (DDD)
• Google Cloud Platform (GCP) / Kubernetes
• Pub/Sub
• PostgreSQL
• React
• GitLab
• Grafana Observability Stack

You are a senior backend engineer with 15+ years of experience building scalable systems, ideally in data-intensive, optimization-driven or algorithm-heavy environments.Technical Knowledge & SkillsStrong backend engineering and system design expertise.Experience with or strong interest in distributed systems, data pipelines or optimization engines.Comfort working on complex, computation-heavy production systems.Fluent in French and professional English.Personal QualitiesAnalytical, ownership-driven and solution-oriented mindset.Strong communication and collaboration skills.Curious engineer with high technical standards.Comfortable in fast-moving, evolving environments.Tech StackWe use a modern, well-crafted tech stack that emphasizes clean architecture, reliability and developer excellence.Languages: Kotlin + SpringBoot, Go, Python Hexagonal architecture / Domain-Driven Design (DDD)Google Cloud Platform (GCP) / KubernetesPub/SubPostgreSQLReactGitLabGrafana Observability Stack BenefitsOne tech conference per year (fully covered)Medium subscription & O'Reilly accessTechnical books & learning resources5% of your time dedicated to exploration & learningHybrid work model, You are a senior backend engineer with 15+ years of experience building scalable systems, ideally in data-intensive, optimization-driven or algorithm-heavy environments.

Technical Knowledge & Skills

• Strong backend engineering and system design expertise.
• Experience with or strong interest in distributed systems, data pipelines or optimization engines.
• Comfort working on complex, computation-heavy production systems.
• Fluent in French and professional English.

Personal Qualities

• Analytical, ownership-driven and solution-oriented mindset.
• Strong communication and collaboration skills.
• Curious engineer with high technical standards.
• Comfortable in fast-moving, evolving environments.

• One tech conference per year (fully covered)
• Medium subscription & O'Reilly access
• Technical books & learning resources
• 5% of your time dedicated to exploration & learning
• Hybrid work model