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Julien GestinJG

Julien Gestin

SENIOR FULL STACK / PLATFORM ENGINEER

€550/day
Saint-Malo, FR
3-7 years

Average response time: 1 hour

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About Julien

Hey 👋


I'm Julien, a freelance Senior Fullstack Engineer & Platform Engineer, specializing in TypeScript, Node.js, NestJS, and React.js/Next.js.

I help startups and SaaS companies design, scale, and secure high-performing web applications capable of handling high traffic, with a strong emphasis on reliability and code quality.

Accustomed to high-volume environments (millions of page views/day, 99.9% SLA), I work on both product and infrastructure/production aspects.

💡 What I Offer


SaaS Applications & Web Products
From architecture to deployment, including front & back-end development

Robust & Scalable Backend
High-performance APIs, modular architecture, load management, caching, message queues

Optimization & Performance
Latency reduction, TTFB improvement, Node.js profiling, database tuning

DevOps & Production
CI/CD, Docker, Kubernetes, ArgoCD, monitoring, observability, alerting

Code Audit & Refactoring
Codebase analysis, technical debt, concrete recommendations

Application Security
OWASP best practices, authentication, secrets management, hardening

🛠️ Stack & Tools


Languages & Frameworks
TypeScript, JavaScript, Node.js, NestJS, React, Next.js

Databases
PostgreSQL, MySQL, MongoDB, Prisma

DevOps / Infra
Docker, Kubernetes, ArgoCD, GitHub Actions, GitLab CI, Terraform

Cloud & Observability
AWS, Scaleway, DigitalOcean, Grafana, Prometheus, Loki

Other
Redis, BullMQ, Nginx, Traefik

📂 Recent Projects

🎮 Real-time quiz/blindtest platform with voice recognition
🛒 High-traffic e-commerce SaaS applications
🚀 Node.js engine optimization handling several million page views/day
⚙️ CI/CD + Kubernetes + ArgoCD setup
  • French

    Native or bilingual

  • English

    Fluent

Remote only
Primarily works remotely

Experience

  • AMUSOIRE
    SENIOR FULL STACK / PLATFORM ENGINEER
    September 2025 - February 2026 (5 months)
    IT DELIVERY AND EXECUTION TASKS :
    • Designed and developed a full-stack application (Blind Test & Quiz) using NestJS (API) and Next.js (frontend), including voice recognition capabilities.
    • Built a License Management System from scratch, covering architecture design, backend services, and user workflows.
    • Implemented GitOps deployment and infrastructure automation using ArgoCD and AWS CDK, improving deployment reliability and repeatability.
    • Refactored backend and frontend to ensure end-to-end type safety, restructured GitLab CI pipelines, and consolidated the codebase within an NX monorepo to improve maintainability and developer productivity.
    NestJs Argo CD AWS CDK Gitlab CI/CD Next.js
  • FASTERIZE
    LEAD BACK END ENGINEER / PLATFORM ENGINEER
    June 2022 - September 2025 (3 years and 3 months)
    IT DELIVERY AND EXECUTION TASKS :
    • Backend technical referent, owning critical architecture decisions, complex debugging, and N3 production incidents.
    • Led optimisation of the Node.js performance engine for a high-traffic platform (millions of page views per day), ensuring a 99.9% SLA and improving API latency and throughput.
    • Developed high-performance APIs with Fastify and built front-end features using Next.js within a fullstack environment.
    • Drove platform stability across a multi-cloud (AWS / Scaleway) environment by reducing high-severity incidents and strengthening observability and incident response.
    • Improved CI/CD pipelines and deployment workflows, cutting release time and increasing delivery reliability.
    ORGANIZATIONAL AND OPERATIONAL LEADERSHIP :
    • Partnered with the CTO on technical hiring: defining profiles, conducting interviews, and evaluating senior engineers.
    • Owned team OKRs and delivery KPIs (quality, lead time, reliability), ensuring alignment between product and engineering.
    Node.js Fastify Next.js Argo CD Gitlab CI/CD
  • ALKANTE
    FULL STACK ENGINEER
    October 2020 - June 2022 (1 year and 8 months)
    • Designed and developed integration bridges between SAP and multiple applications, ensuring reliable data synchronization.
    • Built fullstack features using Angular, Node.js, Symfony, and MySQL.
    Node.js Express Angular

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Education

  • Diploma in Multimedia and Network
    ENSSAT
    2020
    Diploma in Multimedia and Network
  • Master's degree in Telecommunications Engineering
    UPC School
    2020
    Master's degree in Telecommunications Engineering

Skill set

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