Senior Backend Python Engineer - Freelance

Description

Summary: Seeking a backend Python developer to design, develop, and optimize critical payment-related systems for a fast-growing French scale-up, focusing on scalability, reliability, and performance. Highlights: 1. Work on business-critical payment and transaction systems 2. Contribute to resilient microservices architecture 3. Focus on scalability, performance, and transaction reliability ### **Job description** We’re supporting a fast\-growing French scale\-up operating several SaaS products and a B2B marketplace, with strong technical challenges around scalability, reliability, performance, and transaction integrity in an international context. The role is embedded within **payment\-related teams**, working on business\-critical systems that power payment flows, transaction processing, financial data reliability, and integrations with the broader platform ecosystem. ### **Mission – Key Responsibilities (Tech\-focused)** Design, develop, and optimize backend services in Python (FastAPI, Django, or Flask) for **payment and transaction\-related systems**. Contribute to the evolution of a resilient microservices architecture supporting **payment workflows, transaction orchestration, and financial operations**. Build and maintain high\-performance, secure REST/GraphQL APIs connected to **payment services, financial events, and operational flows**. Improve latency, throughput, fault tolerance, and reliability of systems handling **high\-volume payment\-related traffic**. Work on **data consistency, traceability, and transactional flows** in a distributed environment, with strong attention to robustness and accuracy. Help structure and evolve the data model on PostgreSQL and BigQuery for **payment, reconciliation, and operational reporting needs**. Implement and improve CI/CD pipelines with GitHub Actions, Docker, and Kubernetes. Industrialize infrastructure and environments following IaC, observability, and performance best practices. Set up and maintain monitoring \& alerting with Datadog and Sentry, with a strong focus on **critical payment flows, incident detection, and service reliability**. ### **Tech Stack** **Languages / Backend:** Python (FastAPI, Django, Flask) **Databases:** PostgreSQL, BigQuery **Cloud:** GCP (Compute, Pub/Sub, Cloud Run, …) **Observability:** Datadog, Sentry **CI/CD \& Ops:** GitHub Actions, Docker, Kubernetes ### **Profile** 7\+ years of experience in backend Python on complex web architectures. Strong experience with microservices and high\-traffic / scale\-up environments. Solid experience building or maintaining **business\-critical systems related to payments, transactions, billing, or financial flows**. Strong understanding of scalability, performance tuning, monitoring, observability, and **transaction reliability**. Good knowledge of CI/CD and cloud environments, ideally GCP. Product\-oriented mindset, able to balance robust architecture, operational constraints, and business impact. Excellent communication skills and fluent English, comfortable in distributed teams.