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William Balance
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// senior software engineer · seoul, kr · ~/cv

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William Lucien Serge Balance

Senior software engineer · Full-stack · AWS serverless · 7+ years

seoul [email protected] +33 6 69 19 08 93 +82 10 8345 2903 linkedin.com/in/williambalance

01 Résumé

// 7+ years shipping production SaaS

Senior full-stack engineer with 7+ years shipping production SaaS on AWS serverless. Operated as sole engineer running Gayakoa — a multi-tenant event platform serving regulated enterprise clients including Dior, John Deere, Crédit Agricole, Thélem Assurances, Servier, and Comexposium — owning the full stack from React/TypeScript frontend through Node.js Lambda backend to PostgreSQL data layer and CI/CD. In parallel, delivered front-end, back-end, and full-stack work across eight other client engagements (Professeur Caché, YouWho, Galilée, Puzzle System, Ideel, JobConnexion, Wazza, AT Internet), collaborating daily with in-house dev teams, PMs, designers, client-side IT, and other freelancers under Scrum/Kanban. Deep experience shipping document-heavy workflows (media libraries, badges, signatures, billing, ingestion pipelines) and AI-powered features (LLM-generated SQL and analytics, facial recognition, AI translation). Familiar with vendor security questionnaires and audit requirements from banking and insurance clients. Comfortable shaping product and architecture from the ground up.

02 Compétences clés

Languages
TypeScript, JavaScript, Node.js, Python, SQL, C#
Frontend
React, Angular, AngularJS, Ant Design, RTK Query, Redux Toolkit, Shadow DOM, i18n
Backend & Cloud
AWS Lambda, API Gateway (HTTP v2 + WebSocket), PostgreSQL, DynamoDB, RDS, S3, CloudFront, Cognito, SQS/SNS, CloudWatch
IaC & DevOps
Serverless Framework, CloudFormation, GitHub Actions, Docker, Kubernetes, Jenkins
Data
PostgreSQL, Knex.js, Redis, schema migrations at scale
AI integration
Anthropic API (streaming), function calling, RAG, AI document analytics, AI translation, facial recognition
Specialized
Stripe payments, Apple Wallet (PassKit), live video over WebSocket, OAuth 2.0
Collaboration
Scrum, Kanban, cross-functional work with PM/design/client-IT, vendor security questionnaires

03 Expérience

AUG 2018 → PRESENT présent

Software Engineer · Freelance (auto-entrepreneur)

Remote · Seoul, KR / Bordeaux, FR · 7+ years
SEP 2020 → NOW présent

Gayakoa — CTO / sole engineer

Multi-tenant event management SaaS serving enterprise clients across France and internationally. Took over a codebase originally built by a 5–10 dev team and have run product, engineering, and infrastructure single-handedly while interfacing daily with client-side product, marketing, design, and IT teams.

Delivery & scale
  • Delivered several hundred events for enterprise clients including Dior, John Deere, Fédération Française de Football, Servier, Crédit Agricole, Thélem Assurances, Comexposium (SIAL, SIEC, Paris Retail Week, NRF), Truffaut, Intermarché, Altarea, SILMO, SITEVI, ARENA, and Groupe SCAEL
  • Shipped a full back-office rewrite (BO V2) covering 70+ feature modules across attendees, companies, sessions, badges, billing, media, and configuration
  • Designed and shipped matching front-office experiences (FO V1 and V2) with fully configurable per-client branding and multi-language support
Banking & insurance — audit and compliance
  • Onboarded regulated clients (Crédit Agricole, Thélem Assurances) for event management — responded to vendor security questionnaires covering data residency, access control, encryption, incident response, and sub-processor disclosure
  • Coordinated with client-side IT and procurement during integration; produced architecture documentation and security posture summaries on request
AI & document workflows
  • Built an AI feature suite (Maya Builder, Maya Reports) where Claude generates SQL plus interactive HTML widgets rendered safely via Shadow DOM, with RTK Query cache management and sandboxed script execution
  • Implemented facial recognition for on-site attendee check-in and automated badge generation pipelines for printed and digital credentials
  • Built a complete media subsystem: photo session management with shooting workflows, AI-powered filters, taggable file libraries, and CloudFront distribution
  • Implemented AI translation pipelines and a configurable email template engine (v1 to v2) with SMS dispatch via per-tenant gateways
Platform & product
  • Built live event features over WebSocket: real-time video streaming, live audience interaction, and conference signature with regulatory-compliant attendance proof
  • Integrated Stripe Checkout, Apple Wallet .pkpass tickets, and a vouchers, promo codes, teams, and bonus points monetization system
  • Built import pipelines for users and companies including a dedicated Comexposium importer handling format-specific quirks at scale
Infrastructure
  • Split a monolithic serverless.yml into core, features, and monitoring stacks using serverless-plugin-split-stacks, staying under CloudFormation's 500-resource ceiling
  • Designed GitHub Actions CI/CD with parallel deploys across services for fast iteration on a multi-stack project
  • Set up CloudFront CDN, CloudWatch dashboards with PPL-mode log widgets, and 30s WebSocket keepalive eliminating connection drops at scale
  • Operated the full production environment solo: monitoring, incident response, schema migrations, and customer-facing support
stack / TypeScript, Node.js, React, Ant Design, RTK Query, AWS Lambda, API Gateway (HTTP + WS), PostgreSQL, Knex, Serverless Framework, GitHub Actions, Stripe, Anthropic API
MAR 2019 → SEP 2020

Puzzle System — CTO

  • Owned technical direction for a software publishing startup: architecture, hiring decisions, sprint planning under Scrum/Kanban with the in-house team
stack / React, Node.js, AWS, SQL
DEC 2022 → NOW présent

Professeur Caché — Full-stack developer (AWS)

Game and animation studio — built and operated jeu.profcache.fr. Collaborated with the studio's product owner and designers on iterative feature drops.

stack / React, Node.js, AWS
JUL 2022 → AUG 2022

Ideel — Frontend developer

Hightech B2B (ideel.io) — front-end contributions on a React codebase, embedded in the existing dev team.

AUG 2021 → APR 2022

YouWho — Full-stack developer (AWS)

Social network — worked alongside other freelancers and the founding team.

stack / React, React Native, Node.js, TypeScript, AWS
MAR 2021 → JUL 2021

Galilée — Full-stack developer (AWS)

Software publisher (Bordeaux) — contributions inside an existing engineering team.

stack / Node.js, AWS, React
DEC 2018 → MAR 2019

JobConnexion — Backend developer

HR-tech — agile (Scrum/Kanban) with the in-house team.

stack / Node.js, SQL, AWS
SEP 2018 → DEC 2018

Wazza — Frontend developer

Health & wellness — front-end contributions, first paid freelance engagement after graduation.

JUN 2016 → AUG 2018

Full-Stack Developer · Apprenticeship & Internship

AT Internet · Bordeaux, FR · 2 yrs 3 mos
JUN 2016 → AUG 2018

AT Internet — Full-Stack Developer · Apprenticeship & Internship

  • Joined the Rights team owning platform-wide access control and security for AT Internet's web analytics product, used by enterprise clients across Europe
  • Built and maintained features across a polyglot stack: React, AngularJS and Angular, Node.js, and C# .NET, with infrastructure on AWS deployed via Docker, Kubernetes, and Jenkins CI/CD
  • Worked in an agile team (Scrum) with PMs, designers, QA, and senior engineers — progressing from a 4-month internship to a 2-year apprenticeship while completing my Master's at Ynov Education

▸ recap · all engagements

  • SEP 2020 → NOW Gayakoa — CTO / sole engineer
  • MAR 2019 → SEP 2020 Puzzle System — CTO
  • DEC 2022 → NOW Professeur Caché — Full-stack developer (AWS)
  • JUL 2022 → AUG 2022 Ideel — Frontend developer
  • AUG 2021 → APR 2022 YouWho — Full-stack developer (AWS)
  • MAR 2021 → JUL 2021 Galilée — Full-stack developer (AWS)
  • DEC 2018 → MAR 2019 JobConnexion — Backend developer
  • SEP 2018 → DEC 2018 Wazza — Frontend developer
  • JUN 2016 → AUG 2018 AT Internet — Full-Stack Developer · Apprenticeship & Internship

04 Formation · Langues · Licences & certifications

Formation
  • Master's degree, Computer Engineering
    Ynov Informatique
    2014 — 2019
  • Baccalauréat scientifique, Engineering Science
    Lycée Alfred Kastler
    2011 — 2014 · BIA
Langues
  • French Native
  • English Professional
  • Korean Learning
Licences & certifications
  • Private Pilot License (PPL)
    France
William Lucien Serge Balance
Senior software engineer · Full-stack · AWS serverless · 7+ years
Seoul, KR · [email protected] · +33 6 69 19 08 93 · +82 10 8345 2903 · linkedin.com/in/williambalance

// 7+ years shipping production SaaS

01 ─ SUMMARY

Senior full-stack engineer (7+ years). CTO solo of Gayakoa (multi-tenant SaaS for Dior, John Deere, Crédit Agricole, Thélem, Servier, Comexposium — SIAL, NRF, Paris Retail Week). 8 other freelance engagements. Specialized in AWS serverless + AI integration.

02 ─ SKILLS

LANGUAGES
TypeScript, JavaScript, Node.js, Python, SQL, C#
FRONTEND
React, Angular, AngularJS, Ant Design, RTK Query, Redux Toolkit, Shadow DOM, i18n
BACKEND & CLOUD
AWS Lambda, API Gateway (HTTP v2 + WebSocket), PostgreSQL, DynamoDB, RDS, S3, CloudFront, Cognito, SQS/SNS, CloudWatch
IAC & DEVOPS
Serverless Framework, CloudFormation, GitHub Actions, Docker, Kubernetes, Jenkins
DATA
PostgreSQL, Knex.js, Redis, schema migrations at scale
AI INTEGRATION
Anthropic API (streaming), function calling, RAG, AI document analytics, AI translation, facial recognition
SPECIALIZED
Stripe payments, Apple Wallet (PassKit), live video over WebSocket, OAuth 2.0
COLLABORATION
Scrum, Kanban, cross-functional work with PM/design/client-IT, vendor security questionnaires

03 ─ EXPERIENCE

Gayakoa — CTO / sole engineer Sep 2020 → (present)
Delivery & scale
  • Hundreds of events for Dior, John Deere, FFF, Servier, Crédit Agricole, Thélem, Comexposium (SIAL, NRF, SIEC, Paris Retail Week), Truffaut, Intermarché, Altarea, SILMO, SITEVI.
  • Full BO V2 rewrite — 70+ modules (attendees, sessions, badges, billing, media, configuration).
  • Matching FO V1/V2 with fully configurable per-client branding and multi-language support.
Banking & insurance — audit and compliance
  • Onboarded regulated clients (Crédit Agricole, Thélem) — vendor security questionnaires: data residency, encryption, access control, incident response, sub-processors.
  • Architecture documentation and security-posture summaries for client IT and procurement.
AI & document workflows
  • Maya Builder / Reports: Claude-generated SQL + sandboxed HTML widgets via Shadow DOM with RTK Query cache.
  • Facial recognition for on-site check-in and automated badge-generation pipelines (print + digital).
  • Photo-session workflows, AI filters, taggable media library, CloudFront distribution.
  • AI translation pipelines and configurable email/SMS template engine (v1 → v2) per-tenant.
Platform & product
  • Live event over WebSocket — real-time video, audience interaction, regulator-compliant attendance signature.
  • Stripe Checkout, Apple Wallet .pkpass tickets, vouchers/promo/teams/bonus-points monetization.
  • Bulk import pipelines for users/companies, including dedicated Comexposium importer at scale.
Infrastructure
  • Split monolithic serverless.yml into core/features/monitoring stacks (serverless-plugin-split-stacks), under CloudFormation 500-resource ceiling.
  • GitHub Actions CI/CD with parallel deploys across services for fast iteration.
  • CloudFront CDN, CloudWatch dashboards (PPL-mode log widgets), 30s WebSocket keepalive eliminating drops at scale.
  • Solo production ops: monitoring, incident response, schema migrations, customer-facing support.
stack / TypeScript, Node.js, React, Ant Design, RTK Query, AWS Lambda, API Gateway (HTTP+WS), PostgreSQL, Knex, Serverless Framework, GitHub Actions, Stripe, Anthropic API
Puzzle System — CTO Mar 2019 → Sep 2020
  • Technical direction for a software publishing startup — architecture, hiring, sprint planning (Scrum/Kanban) with the in-house team.
  • Owned roadmap and engineering decisions end-to-end while interfacing with founders and clients.
stack / React, Node.js, AWS, SQL
AT Internet — Full-Stack · Apprenticeship & Internship Jun 2016 → Aug 2018
  • Joined the Rights team owning platform-wide access control and security on AT Internet's web analytics product, used by enterprise clients across Europe.
  • Polyglot stack across React, AngularJS / Angular, Node.js and C# .NET — infra on AWS via Docker, Kubernetes and Jenkins CI/CD.
  • Agile (Scrum) with PMs, designers, QA, and senior engineers — progressed from 4-month internship to 2-year apprenticeship while completing Master's at Ynov.

// last updated avr. 2026

William Lucien Serge Balance
Senior software engineer · Full-stack · AWS serverless · 7+ years
Seoul, KR · [email protected] · +33 6 69 19 08 93 · +82 10 8345 2903 · linkedin.com/in/williambalance

// senior software engineer · seoul, kr · ~/cv

01 ─ SUMMARY

// 7+ years shipping production SaaS

Senior full-stack engineer with 7+ years shipping production SaaS on AWS serverless. Operated as sole engineer running Gayakoa — a multi-tenant event platform serving regulated enterprise clients including Dior, John Deere, Crédit Agricole, Thélem Assurances, Servier, and Comexposium — owning the full stack from React/TypeScript frontend through Node.js Lambda backend to PostgreSQL data layer and CI/CD. In parallel, delivered front-end, back-end, and full-stack work across eight other client engagements (Professeur Caché, YouWho, Galilée, Puzzle System, Ideel, JobConnexion, Wazza, AT Internet), collaborating daily with in-house dev teams, PMs, designers, client-side IT, and other freelancers under Scrum/Kanban. Deep experience shipping document-heavy workflows (media libraries, badges, signatures, billing, ingestion pipelines) and AI-powered features (LLM-generated SQL and analytics, facial recognition, AI translation). Familiar with vendor security questionnaires and audit requirements from banking and insurance clients. Comfortable shaping product and architecture from the ground up.

02 ─ CORE SKILLS

LANGUAGES
TypeScript, JavaScript, Node.js, Python, SQL, C#
FRONTEND
React, Angular, AngularJS, Ant Design, RTK Query, Redux Toolkit, Shadow DOM, i18n
BACKEND & CLOUD
AWS Lambda, API Gateway (HTTP v2 + WebSocket), PostgreSQL, DynamoDB, RDS, S3, CloudFront, Cognito, SQS/SNS, CloudWatch
IAC & DEVOPS
Serverless Framework, CloudFormation, GitHub Actions, Docker, Kubernetes, Jenkins
DATA
PostgreSQL, Knex.js, Redis, schema migrations at scale
AI INTEGRATION
Anthropic API (streaming), function calling, RAG, AI document analytics, AI translation, facial recognition
SPECIALIZED
Stripe payments, Apple Wallet (PassKit), live video over WebSocket, OAuth 2.0
COLLABORATION
Scrum, Kanban, cross-functional work with PM/design/client-IT, vendor security questionnaires

03 ─ EXPERIENCE

Software Engineer · Freelance (auto-entrepreneur)
AUG 2018 → PRESENT · (present) · Remote · Seoul, KR / Bordeaux, FR · 7+ years
Gayakoa — CTO / sole engineer SEP 2020 → NOW · (present)

Multi-tenant event management SaaS serving enterprise clients across France and internationally. Took over a codebase originally built by a 5–10 dev team and have run product, engineering, and infrastructure single-handedly while interfacing daily with client-side product, marketing, design, and IT teams.

Delivery & scale
  • Delivered several hundred events for enterprise clients including Dior, John Deere, Fédération Française de Football, Servier, Crédit Agricole, Thélem Assurances, Comexposium (SIAL, SIEC, Paris Retail Week, NRF), Truffaut, Intermarché, Altarea, SILMO, SITEVI, ARENA, and Groupe SCAEL
  • Shipped a full back-office rewrite (BO V2) covering 70+ feature modules across attendees, companies, sessions, badges, billing, media, and configuration
  • Designed and shipped matching front-office experiences (FO V1 and V2) with fully configurable per-client branding and multi-language support
Banking & insurance — audit and compliance
  • Onboarded regulated clients (Crédit Agricole, Thélem Assurances) for event management — responded to vendor security questionnaires covering data residency, access control, encryption, incident response, and sub-processor disclosure
  • Coordinated with client-side IT and procurement during integration; produced architecture documentation and security posture summaries on request
AI & document workflows
  • Built an AI feature suite (Maya Builder, Maya Reports) where Claude generates SQL plus interactive HTML widgets rendered safely via Shadow DOM, with RTK Query cache management and sandboxed script execution
  • Implemented facial recognition for on-site attendee check-in and automated badge generation pipelines for printed and digital credentials
  • Built a complete media subsystem: photo session management with shooting workflows, AI-powered filters, taggable file libraries, and CloudFront distribution
  • Implemented AI translation pipelines and a configurable email template engine (v1 to v2) with SMS dispatch via per-tenant gateways
Platform & product
  • Built live event features over WebSocket: real-time video streaming, live audience interaction, and conference signature with regulatory-compliant attendance proof
  • Integrated Stripe Checkout, Apple Wallet .pkpass tickets, and a vouchers, promo codes, teams, and bonus points monetization system
  • Built import pipelines for users and companies including a dedicated Comexposium importer handling format-specific quirks at scale
Infrastructure
  • Split a monolithic serverless.yml into core, features, and monitoring stacks using serverless-plugin-split-stacks, staying under CloudFormation's 500-resource ceiling
  • Designed GitHub Actions CI/CD with parallel deploys across services for fast iteration on a multi-stack project
  • Set up CloudFront CDN, CloudWatch dashboards with PPL-mode log widgets, and 30s WebSocket keepalive eliminating connection drops at scale
  • Operated the full production environment solo: monitoring, incident response, schema migrations, and customer-facing support
stack / TypeScript, Node.js, React, Ant Design, RTK Query, AWS Lambda, API Gateway (HTTP + WS), PostgreSQL, Knex, Serverless Framework, GitHub Actions, Stripe, Anthropic API
Puzzle System — CTO MAR 2019 → SEP 2020
  • Owned technical direction for a software publishing startup: architecture, hiring decisions, sprint planning under Scrum/Kanban with the in-house team
stack / React, Node.js, AWS, SQL
Professeur Caché — Full-stack developer (AWS) DEC 2022 → NOW · (present)

Game and animation studio — built and operated jeu.profcache.fr. Collaborated with the studio's product owner and designers on iterative feature drops.

stack / React, Node.js, AWS
Ideel — Frontend developer JUL 2022 → AUG 2022

Hightech B2B (ideel.io) — front-end contributions on a React codebase, embedded in the existing dev team.

YouWho — Full-stack developer (AWS) AUG 2021 → APR 2022

Social network — worked alongside other freelancers and the founding team.

stack / React, React Native, Node.js, TypeScript, AWS
Galilée — Full-stack developer (AWS) MAR 2021 → JUL 2021

Software publisher (Bordeaux) — contributions inside an existing engineering team.

stack / Node.js, AWS, React
JobConnexion — Backend developer DEC 2018 → MAR 2019

HR-tech — agile (Scrum/Kanban) with the in-house team.

stack / Node.js, SQL, AWS
Wazza — Frontend developer SEP 2018 → DEC 2018

Health & wellness — front-end contributions, first paid freelance engagement after graduation.

Full-Stack Developer · Apprenticeship & Internship
JUN 2016 → AUG 2018 · AT Internet · Bordeaux, FR · 2 yrs 3 mos
AT Internet — Full-Stack Developer · Apprenticeship & Internship JUN 2016 → AUG 2018
  • Joined the Rights team owning platform-wide access control and security for AT Internet's web analytics product, used by enterprise clients across Europe
  • Built and maintained features across a polyglot stack: React, AngularJS and Angular, Node.js, and C# .NET, with infrastructure on AWS deployed via Docker, Kubernetes, and Jenkins CI/CD
  • Worked in an agile team (Scrum) with PMs, designers, QA, and senior engineers — progressing from a 4-month internship to a 2-year apprenticeship while completing my Master's at Ynov Education

04 ─ EDUCATION · LANGUAGES · CERTIFICATIONS

EDUCATION
  • Master's degree, Computer Engineering
    Ynov Informatique
    2014 — 2019
  • Baccalauréat scientifique, Engineering Science
    Lycée Alfred Kastler
    2011 — 2014 · BIA
LANGUAGES
  • French — Native
  • English — Professional
  • Korean — Learning
CERTIFICATIONS
  • Private Pilot License (PPL)
    France

// last updated avr. 2026 · cv version detailed