Website: [https://www.bailleul.dev](https://www.bailleul.dev) # Guillaume Bailleul **Senior Full-Stack Software Engineer — Go/Python, React, and Distributed Systems** Lille, France · +33 7 81 79 29 34 · [guillaume.bailleul@gmail.com](mailto:guillaume.bailleul@gmail.com) · [LinkedIn](https://www.linkedin.com/in/bailleul-dev/) · [GitHub](https://github.com/bailleul-dev) --- ## Professional Summary Senior full-stack software engineer with 15 years of experience designing and shipping complete products: Go and Python backends, APIs, and distributed systems on the server side, React and React Native applications on the client side. My background spans IoT platforms, a very-high-scale email delivery API, a document management solution, a maritime AI platform, and HR products. My consistent focus has been transforming complex business requirements and existing systems into robust, scalable, and maintainable services. My full-stack profile builds on Go and Python on the server side, backed by deep Elixir experience, and on TypeScript, React, Next.js, and React Native on the client side. Accustomed to contributing from architecture through delivery in international teams and business-critical production environments, I combine long-term thinking with pragmatic execution. --- ## Professional Experience ### Senior Software Developer **Andjaro** | Paris, Ile-de-France, France (Remote, English) | October 2021 - April 2026 Following Andjaro's acquisition by Silae in 2023, I successively worked within two product teams. #### Silae HR Suite | 2024 - 2026 HRIS SaaS solution for small and mid-sized companies, covering HR processes from hiring to payroll preparation and used by more than 2,000 customers to manage approximately 230,000 employment contracts per year. - Progressively modernized critical legacy Symfony components, including Claude-assisted analysis and refactoring of design issues, while preserving production stability - Designed a Python/FastAPI agentic workflow based on LangGraph to explain payroll items, reducing the related customer support backlog by 80% - Improved the reliability of AI-assisted development through stronger tests, Claude policies, reusable skills, Model Context Protocol (MCP), and subagents - Prototyped internal DevOps tools in Go, then led technical discussions comparing Communicating Sequential Processes (CSP), Elixir's actor model, and the event loops of Node.js and Python - Supported six team members with no prior Claude experience through the adoption of generative AI despite strong initial reluctance - Designed integrations with payroll systems, ERP platforms, planning tools, and HRIS platforms Technologies: Python, FastAPI, Go (R&D), Symfony, PostgreSQL, Docker, Kubernetes, LangGraph, MCP, Claude #### Andjaro Platform | 2021 - 2024 Workforce management platform for healthcare, the public sector, retail, and facility management. - Developed and evolved core HR platform features in Elixir/Phoenix - Co-designed business workflows and React interfaces tailored to the French Ministry of Education - Collaborated remotely within an international, English-speaking engineering team Technologies: Elixir, Phoenix, React, Symfony, PostgreSQL, Kafka, Docker, Kubernetes ### Independent Software Engineer **Independent (Pagily)** | Lille Region, France | December 2019 - October 2021 Pagily is a document management platform dedicated to paperless workflows, universal scanning, and secure printing. - Led the technical direction, architecture decisions, and product delivery - Designed .NET/C# backend services using a modular architecture based on dependency injection, layered services, and microservice patterns for secure document processing and indexing - Developed the web application in React and Next.js, as well as the mobile application in React Native - Implemented an automated document classification and indexing pipeline - Designed integrations with multifunction printers and scanning equipment Technologies: .NET/C#, React, Next.js, React Native, PostgreSQL ### Software Developer **Shipfix (Veson Nautical)** | Paris, Ile-de-France, France (Remote, English) | April 2019 - November 2019 Shipfix was a startup developing an AI-driven platform for maritime chartering and operations. - Rapidly delivered end-to-end product features, from Python and Elixir backend services to the React Native mobile application - Developed a Python/FastAPI API for email parsing and data extraction - Designed interactive opportunity-matching workflows, collaboration tools, and real-time analytics features Technologies: Python, FastAPI, Elixir, React Native, PostgreSQL, Docker ### Senior Software Developer **Agence Dernier Cri** | Lille Region, France (Remote, English) | August 2016 - April 2019 #### Mailjet SendAPI v3.1 - Architected and implemented Mailjet SendAPI v3.1 in Go - Delivered on an existing GCP infrastructure a distributed API capable of handling millions of email delivery requests - Integrated Cassandra message storage with legacy Free Pascal systems Technologies: Go, PostgreSQL, Docker, GCP, Cassandra #### Leroy Merlin Monitoring Platform - Designed a real-time monitoring system with an Elixir/Phoenix backend and React Native application - Designed high-frequency ingestion pipelines for multiple business entities Technologies: Elixir, Phoenix, React Native, PostgreSQL, Docker #### Multi-Business-Unit Data Platform — ADEO - Designed an internal platform enabling each business unit to define its own data schemas through an API - Implemented data validation, consistency, and integrity controls before persistence - Designed an inter-business-unit authorization system that restricted each entity to data it had been granted permission to access - Delivered the MVP of this strategic project on schedule as part of a team assembled specifically for the project and bringing together contractors from several companies Technologies: Node.js, MongoDB #### Consulting Engagements - Cityscoot: architected APIs capable of handling high loads generated by mobile usage - Les Hôtels très particuliers: stabilized legacy systems, reduced technical debt, and transferred knowledge to the team Technologies: Python, Go, Node.js, React, React Native, Cassandra, PostgreSQL, Elixir ### Software Developer **Elicity/Xee** | Lille, France | December 2013 - July 2016 Xee developed an IoT platform connecting an in-car device, cloud services, APIs, and third-party applications. - Designed and developed an IFTTT-like event automation engine for the XeeCLOUD platform - Migrated data from MySQL to Cassandra and MongoDB to adapt storage to new use cases and volumes - Progressively modernized a Symfony 2 monolith into Go, Python, and Node.js microservices, including rewriting the Doctrine 2 persistence layer as a high-performance Go REST API - Architected and developed a high-traffic distributed IoT platform based on microservices and event-driven processing with RabbitMQ - Improved production reliability by maintaining the historical API, redesigning push notifications, and automating the CI/CD pipeline with Docker, Jenkins, and Ansible Technologies: Go, Python, Node.js, RabbitMQ, Cassandra, MongoDB, MySQL, Docker, Jenkins, Ansible, Symfony 2 --- ### Software Developer **EDF** | Lille, France | September 2011 - August 2013 Designed and developed a call-performance monitoring tool for EDF customer contact centers, initially deployed regionally and later rolled out nationwide. - Automated data extraction from the existing call-tracking software - Aggregated and calculated performance indicators from multiple data sources - Developed a real-time dashboard to display key performance indicators (KPIs) in customer contact centers Technologies: .NET, MySQL ## Education **Master's degree in Computer Engineering** — EFFICOM Lille | 2013 **Professional Bachelor's degree in Industrial Computing and Networks (IRI)** — IUT A de Lille | 2011 ## Technical Skills **Architecture and backend**: REST API design, microservices, distributed systems, event-driven processing, business integrations, and legacy system modernization. **Backend languages**: Go, Python, Elixir, TypeScript/Node.js, C#, and PHP. **Backend frameworks**: Phoenix/OTP, FastAPI, .NET, and Symfony. **Web and mobile**: React, React Native, TypeScript, Vue.js, and Next.js. **Data and messaging**: PostgreSQL, Cassandra, MongoDB, MySQL, Kafka, and RabbitMQ. **Cloud and delivery**: delivery of services to existing Google Cloud Platform (GCP) infrastructure, Docker, Kubernetes, CI/CD, Jenkins, and Ansible. **Agentic AI**: workflow design with LangGraph, MCP integrations, and AI-assisted development with Claude. --- ## Key Achievements - Architected and implemented Mailjet SendAPI v3.1 in Go, a distributed API handling millions of email delivery requests - Modernized the XeeCLOUD IoT platform through data migrations, progressive extraction from the Symfony monolith, and development of event-driven services - Led the architecture and delivery of Pagily, from its .NET document services to its React and React Native applications - Designed critical integrations with payroll systems, ERP platforms, planning tools, HRIS platforms, and scanning equipment - Designed an agentic workflow explaining payroll items, reducing the related support backlog by 80% --- ## Languages - French: Native - English: Professional working proficiency — used both verbally and in writing within international and distributed teams - Remote collaboration with English, Spanish, Ukrainian, and Russian colleagues