Staff Backend Engineer & Platform Engineer specialized in high-throughput payment systems, event-driven architectures, and GraphQL APIs. 12+ years of experience across fintech, e-commerce, and SaaS.
Paris, France | French | vangout.cedric@gmail.com | Calendly | LinkedIn | GitHub
- 50x throughput on a EU payment processor — 100K req/min under 15 ms (SysPay)
- Shipped PrestaShop's SaaS platform after 3 failed attempts, onboarding 100+ merchants
- GDPR + HL7 health-data API — security audit: zero blocking findings (PromTime)
- Top #2 contributor to supabase-community/postgres-language-server
- TypeScript, Rust, Node.js, PostgreSQL, GraphQL, Performance Engineering
- Node.js, Bun, Deno, Hono, Rust, Axum, Python, FastAPI, HTMX
- GraphQL (federation, graphql-yoga), REST, gRPC, OpenAPI, webhooks, Hasura, Supabase
- PostgreSQL (CDC, RDS Proxy, indexing, slow-query optimization), MongoDB, Redis
- Kafka, event streaming, message queues
- CPU / RAM / IO profiling, load testing (k6), hot path isolation
- Clean Code, TDD, Hexagonal Architecture (Ports & Adapters), Domain-Driven Design (DDD)
- Event-Driven Architecture, CQRS, Microservices, BFF, ADRs
- AWS (API Gateway, Lambda, ECS, RDS Proxy, RDS, SNS, SQS, X-Ray, S3), GCP (Cloud Run)
- Terraform, AWS CDK, Docker, GitHub Actions, GitLab CI
- OpenTelemetry, Grafana, ClickHouse, HyperDX
- PCI-DSS, PSD2, SCA, 3D Secure, GDPR, HL7
Short backend engagements and AI-adoption consulting for startups.
- Claude Code / Cowork setup in IDE and GitHub CI for automated code reviews
- Short-term backend development (Node.js, TypeScript, PostgreSQL)
Tech stack: Node.js, TypeScript, PostgreSQL, Claude Code, GitHub Actions
Settleflow is a Stripe-like payment processor handling millions of payment requests per day across Europe, with a reconciliation layer running in the background (settleflow.io).
Challenge: Serve very high payment traffic under 15 ms latency, on a serverless stack, under PCI-DSS constraints.
Designed the event-driven architecture and cloud infrastructure for the payment processor, within a team of 5 engineers:
- Event-driven architecture built on PostgreSQL CDC replication (aws_lambda extension) synced to AWS SNS and consumed by AWS Lambda functions
- Webhook delivery to partners and billing/analytics metrics fed from the payment event stream
- Infrastructure built entirely with Terraform modules and PCI-DSS-compliant AWS services (KMS, encrypted RDS, RDS Proxy, segmented VPC, Lambda, security groups, IAM)
- Stripe-like public API with background reconciliation processing
- VAMP Ratio (Visa Acquirer Monitoring Program) monitoring to track fraud and dispute ratios against Visa compliance thresholds
- PSD2 Strong Customer Authentication (SCA) via 3D Secure for EU card payment flows, ensuring regulatory compliance
- Moved non-critical SQL queries off the hot path into background jobs
- Continuous PostgreSQL optimization: enabling and resolving slow query logs, monitoring CPU load (cache) and max connections (Lambda concurrency)
- Built a CI/CD automation CLI (ARGC, Rust) deeply integrated with GitLab CI, deploying each MR to an ephemeral environment with a seeded database in under one minute
- Git tag-triggered production deployments with automatic CHANGELOG updates (release notes extracted from commits)
- Pipeline linter integration: OXC (TypeScript) and Squawk (detecting dangerous or slow PostgreSQL migrations in production)
- Load regression tests (k6) run on every MR and release
- Enforced clean code standards (SOLID, small reviewable PRs, OXC lint gate) across the team of 5
- Structured Lambda handlers with a hexagonal (ports & adapters) design, isolating payment domain logic from AWS-specific I/O for testability
- Modeled the payment domain (transactions, reconciliation, webhooks) as bounded contexts to keep core business logic AWS-agnostic
- Documented key architecture decisions (event-driven CDC pipeline, Lambda concurrency model) in ADRs
- Served up to 100,000 payment requests per minute under 15 ms, with 900 concurrent Lambdas and an RDS Proxy pool fronting a scaled RDS instance
- ~50x throughput improvement by choosing auto-scaling Lambdas over EC2 instances
- Reduced SQL queries per application request from 150+ to under 15 through dedicated PostgreSQL indexes
- Seeded ephemeral environments adopted by all contributors, accelerating iteration and regression review
Tech stack: TypeScript, Bun, Hono, OpenAPI, Swagger Codegen, Rust, ARGC, OXC, Squawk, PostgreSQL (CDC, aws_lambda extension, RDS Proxy), AWS (Lambda, encrypted RDS, KMS, VPC, security groups, IAM, SNS), Terraform, AWS CDK, Bash, k6, GitLab CI/CD, PCI-DSS, PSD2, SCA, 3D Secure, OpenTelemetry
PrestaShop is the open-source e-commerce platform for creating and managing online stores; the project aimed to build its SaaS version (onboarding.prestashop.com).
Challenge: Ship the SaaS version of PrestaShop after three failed attempts, coordinating four squads with conflicting priorities.
Led the "onboarding" squad (5 engineers) and built the SaaS version of PrestaShop, collaborating with the "core", "accounts", "billing", and "hosting" squads:
- Designed and implemented a GraphQL gateway (graphql-yoga, graphql-codegen) federating 4 internal micro-services (onboarding, accounts, billing, hosting) under a unified BFF for the Vue frontend
- Generated a type-safe GraphQL client from the schema, producing typed Vue hooks
- GitHub Actions pipeline running GraphQL Inspector (graphql-inspector) to detect schema bugs, breaking changes, and regressions, plus tests, then publishing a Docker image to GCP Cloud Run
- Proposed the initial architecture for onboarding.prestashop.com, jointly with the engineering manager
- Wrote architecture decision records (ADR), enforced clean code standards via code review, and mentored junior developers in the squad
- Led architecture meetings with tech leads from other squads to present the target architecture and arbitrate integration points and workflow dependencies
- Aligned squad boundaries (onboarding, accounts, billing, hosting) with DDD bounded contexts to minimize cross-service coupling in the GraphQL gateway
- Contributed to PrestaShop's open-source codebase to add generic extension points tailored to our needs
- Reverse-engineered and contributed (MRs) to other squads' codebases to meet deadlines and shared objectives
- Shipped ahead of schedule, onboarding 100+ merchants
- GraphQL approach adopted by other squads in their codebases
Tech stack: TypeScript, Node.js, GraphQL (graphql-yoga, graphql-codegen, graphql-inspector, federation, BFF), Vue.js, GCP (Cloud Run), Docker, GitHub Actions
elba is an all-in-one cybersecurity hub designed to secure teams in their daily work (elba.security).
Embedded in a team of 5 engineers working directly with the CTO, responsible for developing a standalone feature, the "Training" module:
- Delivered the "Training" module end-to-end: a 50+ step form assessing users' security knowledge (1,000+ users), consuming the Hasura GraphQL API and persisting progress incrementally, with React pages built on the internal design system
- Migrated the application to an event-driven approach using Hasura event triggers
- Built a Segment connector (Hasura event listener) forwarding relevant events — made seamless since every action was natively an event
Tech stack: TypeScript, Node.js, React, PostgreSQL, Hasura, Segment, Vercel, GitHub Actions
Theodo FinTech builds innovative digital applications for the finance sector.
Embedded in a team of 3 engineers, contributing to internal administration tools (employee management portal):
- Developed an employee profile management page within the internal portal
- Extended the GraphQL API to cover new requirements
- Set up an auto-generated GraphQL client via graphql-codegen
- Added pages and components to the React codebase
- Verified the Kafka integration to ensure proper event propagation for new features within the CQRS architecture
Tech stack: Node.js, TypeScript, GraphQL, Apollo Server, React, MongoDB, Kafka, CQRS
PromTime is a data science company that compares patient health outcomes in real time (promtime.org).
Challenge: Ingest high-volume patient health data following the complex PROM specification, under GDPR and HL7 constraints.
Embedded in a team of 3 engineers working directly with the CTO, selected for my GraphQL expertise to build a high-volume data ingestion API (PROMs):
- Studied the PROM specification to propose a pragmatic GraphQL schema (300+ fields) bridging fixed and dynamic data
- Built the GraphQL ingestion API (Apollo Server) with an interactive playground
- Designed the GraphQL server in compliance with GDPR requirements and the HL7 standard
- Wrote detailed documentation for partners: the PROM specification being complex, accurate field mapping is critical for business operations
- 20 partners connected, collecting ~2,000 patient records/day
- Security audit passed with no blocking findings
Tech stack: TypeScript, Node.js, GraphQL, Apollo Server, PostgreSQL, GCP, Bitbucket, GDPR, HL7
Freelance engagements embedded in client teams, working with startups, scale-ups, and large enterprises in fintech, real estate, mobility, and e-commerce (full-stack and mobile development).
Worked as a developer and tech lead across multiple engagements:
- SNCF Connect & Tech: hired for my GraphQL expertise, built a complex multi-step form on AWS Amplify; designed the GraphQL schema and technical architecture
- Piteo (Tech Lead): led the architecture of a GraphQL API enabling landlords to manage their real estate portfolio; set up cloud infrastructure from scratch (Heroku) and CI/CD pipelines
- LSF Énergie: built a Python scraper integrating Google Vision OCR to automate employee workflows; set up GCP infrastructure and production monitoring
Tech stack: TypeScript, Node.js, GraphQL, React, Python (Google Vision OCR), PostgreSQL, AWS (Amplify), GCP, Heroku, GitHub Actions, GitLab CI
jestocke.com is a peer-to-peer online marketplace for renting unused storage spaces (jestocke.com).
Challenge: Build the critical components of a growing marketplace with a two-person engineering team.
- Built the listing search engine (Algolia) and peer-to-peer booking and payment system (MangoPay)
- Managed and monitored the production infrastructure (Heroku)
- Helped structure the engineering team and recruited new members
- 20K+ listings indexed, 100K+ transactions processed
- Engineering team grown from 2 to 5 developers
- Startup grown from 3 to 10+ employees through its second funding round (€2M)
Tech stack: Python, Django, PostgreSQL, Heroku, MangoPay, Algolia
- supabase-community/postgres-language-server — A Language Server for PostgreSQL. Top #2 contributor.
| English | Native or bilingual proficiency |
| French | Native or bilingual proficiency |
| 2012 - 2014 | EPSI – BTS Services informatiques aux organisations (Programmation) |
| 2014 - 2015 | WIS – Bachelor Chef de Projet Digital (Management de projet) |
- Mouad Chaouki - Tech Lead (SysPay)
- Gautier Boudeweel - Engineering Manager (PrestaShop)
- Antoine Berton - CTO (elba)
- Alexandre Blondin - Tech Lead (Theodo FinTech)
- Loic Calvy - CTO (PromTime)
- Laure Courty - CEO (jestocke.com)