Сергій

Serhii Sierov
JavaScript & TypeScript Software Engineer
𝟮𝟰 𝘆𝗲𝗮𝗿𝘀 𝗶𝗻 𝗜𝗧: I started by building and maintaining the foundations of technology -
hardware, networks, operating systems, and software. Today, I architect & develop
enterprise-grade AI and SaaS solutions in the cloud, driven by the same curiosity and
commitment to continuous growth that started my journey.

Github: https://github.com/serhii-sierov

| SUMMARY Technical Proficiencies
LANGUAGES
I transform complex business
TypeScript, JavaScript, Terraform, Bash
challenges into scalable SaaS,
AI-powered, web, and mobile CLIENT-SIDE
products that automate business React, Next.js, Redux, React Query, React Native, Apollo GraphQL
processes, expand into new
SERVER-SIDE
markets, and create long-term
Node.js, Express, NestJS, Sequelize, TypeORM, Prisma, Bull Module
competitive advantage.
DATABASES
I’ve architected and developed
MySQL, PostgreSQL, MongoDB, Firestore, Supabase
software solutions across
healthcare, veterinary, mental USER INTERFACE
wellness, hearing therapy, retail, Ant Design, Bootstrap, Material UI, TailWind, CSS, Sass, Less
e-commerce, weather
intelligence, and AI content TESTING LIBRARIES
Jest, React Testing Library, Postman, Playwright
creation.
CLOUD SERVICES
A few of key results achieved:
AWS (EC2, Fargate, S3, RDS/Aurora, ElastiCache, ECR, SES), GCloud (CloudRun, Functions),
➔ 30% faster feature delivery Vercel, CloudFlare (DNS, ZeroTrust, ALB)

through microservices CI & CONTAINERIZATION
migration. Docker, Jenkins, Webpack, GitHub Workflows
➔ 60% reduction in content
creation costs using AI AI & INTEGRATIONS
automation OpenAI, Anthropic Claude, Mistral, LiveKit, Stripe, Twilio, DocuSign, Google APIs, Auth0
➔ 40% faster API responses
through caching and Employment History
architecture optimization SysGears (October 2020 - Present)
➔ scaled AI-powered app to Senior JavaScript & TypeScript Software Engineer – Web & Mobile Development
10,000+ daily active users - Leading full-stack development of SaaS, web, and mobile products with React, Next.js, React
➔ built and operated Native, NestJS, and TypeScript
enterprise SaaS platforms - Designing scalable architectures, including monolith-to-microservices migrations
with 240+ integrated tools - Building AI-powered features using OpenAI, Anthropic Claude, and other LLMs for content
and AWS cloud generation, analysis, and workflow automation
infrastructure - Developing multi-tenant platforms with RBAC, secure authentication, partner isolation, and
enterprise-grade access control
- Architecting and documenting REST, GraphQL, and SDK APIs with strong typing,
OpenAPI/Swagger documentation, and shared TypeScript contracts
- Creating reusable UI libraries, shared packages, and monorepo solutions to accelerate
delivery across teams and products

| AREAS OF EXPERTISE - Designing cloud-native solutions on AWS, including ECS, RDS, Redis, S3, Lambda, CI/CD
pipelines, and Infrastructure as Code with Terraform
● End-to-end development of
- Optimizing application performance through caching, background jobs, horizontal scaling,
scalable web and mobile
and infrastructure cost improvements
applications - Implementing analytics, feature flags, localization, notification systems, and other
● Design of scalable system product-growth capabilities
architectures including - Establishing engineering standards through code reviews, testing strategies, CI/CD
microservices, multi-tenant automation, and architecture best practices
SaaS, REST/GraphQL APIs, - Collaborating directly with stakeholders to turn business requirements into scalable technical
and modular backend solutions
systems - Mentoring engineers and contributing to technical leadership across distributed Agile teams
● Integration of AI/LLM
capabilities into production SysGears (March 2016 - September 2020)
systems for content JavaScript & TypeScript Software Engineer
- Translating high-level business requirements into scalable full-stack applications
generation, automation,
- Developing SaaS platforms with React, Next.js, Firebase, and NestJS
analytics, and user-facing
- Building custom tools like AI-assisted content editors and smart weather apps
features
- Integrating third-party APIs like Stripe, Algolia, and external weather data providers
● Cloud-native architecture
- Improving backend performance through Redis caching and architecture refactoring
and deployment on
- Designing and managing PostgreSQL, MongoDB, and MySQL schemas for dynamic data
AWS/GCP (ECS, Lambda, modeling
RDS, S3, Cloud Run), with - Writing unit and E2E tests with Jest and React Testing Library to maintain code reliability
CI/CD automation, Docker - Containerizing apps with Docker and deploying to AWS services (S3, EC2, Elastic Beanstalk)
containerization, Terraform - Collaborating with product teams and designers to deliver polished UX and maintainable
IaC code
- Contributing to DevOps processes and CI setup to streamline team workflows

| EDUCATION FOXOPTICA (April 2021 - February 2022)
Owner & Technical Lead
Kherson National Technical - Managing procurement operations across warehouse stock and on-demand fulfillment
University - Leading employee training and qualification to maintain operational standards
- Owning development and maintenance of the business website (Next.js, Nest, Apollo
Specialty Computer Science GraphQL)
Degree Master’s
Gravis (2008 - March 2021)
Co-owner & Technical Lead
- Leading and managing the team, overseeing day-to-day business operations
- Managing direct client relationships and translating business needs into solutions
- Architecting, developing, and maintaining the business platform (PHP, HTML, CSS, REST API)
- Coordinating core business processes and driving operational improvements

UKRSKLOPROM (2002 - 2009)
System Administrator, 1C Developer
- Administering Windows Server, Active Directory, and Linux infrastructure
- Developing and maintaining business solutions in the 1C Accounting System
- Managing company-wide hardware infrastructure and IT operations

ARBATSKAYA STRELKA (2002 - 2002)
C++ Developer
- Developing and maintaining cash machine drivers using C++ and Win32

Notable Projects

| AI-Driven Pet Health System
(the name is under NDA)

A multi-tenant AI-powered veterinary practice management SaaS designed for clinics, pet owners, and
enterprise veterinary groups. The platform provides a complete ecosystem with dedicated portals for clinics,
consumers, enterprises, administrators, and referrals, covering EMR workflows, appointment scheduling,
treatment management, billing, telemedicine, insurance processing, and AI-assisted veterinary support with
240+ integrated tools. The solution helped veterinary organizations automate daily operations, improve service
quality, reduce administrative workload, and securely scale their digital infrastructure.

Responsibilities
- Leading full-stack development across a complex multi-tenant SaaS platform, translating product
requirements into scalable technical solutions across frontend, backend, AI, and infrastructure
- Architecting and delivering business-critical platform capabilities, including flexible RBAC, infrastructure
cost analysis, and other core product enhancements
- Owning the AWS infrastructure architecture & implementation across prestaging, staging, and
production environments, including ECS Fargate, VPC, ALB, RDS, Redis, S3, SES, Secrets Manager, and
GitHub OIDC deployment roles, with Terraform
- Architecting and maintaining CI/CD with 30+ GitHub Actions workflows, implementing path-based
deployments, 3-tier environment promotion, hotfix synchronization, merge-queue E2E quality gates,
SonarCloud/CodeQL checks, and reusable composite actions
- Designing and implementing automated credential rotation, using AWS Lambda to synchronize
RDS/Redis credentials with application secrets and trigger zero-downtime ECS rolling restarts
- Designing secure developer and production data-access workflows through AWS SSM Session
Manager, PostgreSQL, Redis, and Aurora Global, including reader/writer IAM enforcement and
SSO-based developer onboarding automation
- Architecting and maintaining AWS IAM Identity Center (SSO) with capability-based Permission Sets,
enforcing separation between deployment, data, and secrets access in alignment with GDPR and HIPAA
requirements
- Driving technical discussions and architecture decisions with cross-functional teams, balancing
scalability, security, maintainability, and infrastructure costs
- Establishing and maintaining engineering standards across code quality, testing, CI/CD, infrastructure,
and production operations
- Supporting team onboarding and knowledge sharing, helping engineers understand the architecture,
development workflows, infrastructure, and engineering standards

Technology Stack
Next.js 15, React 19, TypeScript, Tailwind CSS 4, React Query, Redux Toolkit, NestJS 11, Prisma 7, PostgreSQL,
Redis, BullMQ, Socket.IO, OpenAI, Anthropic Claude, Mistral, LiveKit, Stripe, Twilio, DocuSign, AWS (ECS, EKS,
RDS, ElastiCache, S3, Secrets Manager, SES, Lambda), Docker, GitHub Actions, ECR, OIDC, SonarCloud,
CodeQL, E2E (Bun + Playwright), Husky pre-commit hooks, Sentry

| Hearing assessment and therapy SDK API
(the name is under NDA)

A backend API that powers an SDK for hearing therapy, designed for smooth integration into both mobile and
web apps. This application is a suite of software-based diagnostics and therapies – aimed at preserving hearing,
restoring auditory function, and relieving tinnitus.

The system is architected as a modern monorepo, featuring a scalable backend powered by NestJS and
Firebase Functions. It includes robust user management, partner integration, hearing assessments, and therapy
session tracking. An admin CMS - built with React and FireCMS - enables efficient data management. The
platform ensures high data integrity using application-level referential constraints in Firestore, and includes
comprehensive test coverage with Jest. CI/CD pipelines with semantic versioning streamline deployment.

With support for multi-tenant architecture and API key-based authentication, the platform enables type-safe
integration across frontend and backend via shared TypeScript types. It also features detailed
Swagger/OpenAPI documentation for interactive API testing, schema validation, and custom configuration
options.

Responsibilities
- Architecting and leading backend development of a modular NestJS API comprising 8 core domains:
User, Partner, Assessment, Therapy Session, Program, UserProgram, SDK Log, and Health
- Designing the system architecture around layered Controllers → Services → Repositories, ensuring clear
separation of concerns and long-term maintainability
- Designing the multi-tenant architecture with partner isolation, permission management, and API
key-based authentication for secure external integrations
- Architecting Firestore data relationships with application-level referential integrity, foreign-key
validation, and data consistency controls
- Designing and implementing REST APIs with consistent validation, pagination, HTTP status handling,
structured errors, and standardized API responses
- Establishing a TypeScript monorepo architecture with shared types and interfaces across the API and
React-based CMS, ensuring type-safe integration between backend and frontend
- Designing and implementing partner-facing SDK capabilities, enabling external applications to integrate
hearing assessments and therapy workflows through a consistent, documented API
- Implementing optimistic concurrency control for program versioning to maintain data consistency
across concurrent updates
- Leading API documentation and contract definition through comprehensive OpenAPI/Swagger
specifications, schema validation, and interactive API testing
- Architecting and implementing the automated testing strategy, covering Jest unit tests, mocked
scenarios, Postman integration tests, and end-to-end validation
- Designing and maintaining CI/CD workflows with GitHub Actions for automated testing, deployment,
and semantic versioning
- Architecting and configuring the Firebase/GCP infrastructure, including Firebase Functions, Firestore,
and hosting environments
- Leading development of the React/Firebase-based admin CMS with FireCMS for efficient management
of users, partners, assessments, programs, and therapy data
- Establishing engineering quality standards through strict TypeScript typing, ESLint, Prettier, pre-commit
hooks, automated validation, and comprehensive test coverage

- Driving technical decisions and implementation across backend, frontend, API contracts, infrastructure,
testing, and deployment
- Supporting knowledge transfer and onboarding, helping engineers understand the system architecture,
shared contracts, development workflows, and engineering standards

Technology Stack
Firebase (Functions/Firestore), GCloud, NestJS, React, TypeScript, Jest, CI/CD

| AI Mental healthcare system
(the name is under NDA)

A mobile application that uses AI algorithms to help users maintain their mental health. Users fill in information
about their state, and the application analyzes it and provides helpful advice and exercises to improve users’
mental well-being.

The work on the project is organized following the SCRUM framework. The main goals were to redesign the
existing application, add new features, and improve user experience. The project was transferred from
monolithic to microservice architecture to ensure easier scaling and maintenance. There was a need to create a
UI library with cross-platform components to reuse among all the services and an analytics service to track
users’ actions and analyze statistics. Both packages are published using the NPM register.

View full case study →

Responsibilities
- Led the technical modernization of the production application, migrating the system from a monolithic
architecture to microservices to improve scalability, maintainability, and independent service evolution
- Architected and implemented new microservice capabilities across React, React Native, Next.js, NestJS,
Node.js, and GraphQL
- Designed and built a reusable cross-platform UI library, enabling consistent components and faster
feature delivery across multiple services and platforms
- Architected and implemented an analytics service to capture user behavior and provide data for
product and engagement decisions
- Integrated ChatGPT for automated dream analysis, delivering personalized AI-powered insights and user
experiences
- Designed and implemented real-time remote configuration, enabling feature toggling and configuration
changes without requiring application redeployments
- Implemented timezone-based user segmentation for targeted push notifications, improving the timing
and effectiveness of user engagement
- Designed and implemented dynamic localization with Lokalise, enabling language updates without
requiring new application releases
- Engineered backward compatibility across millions of users running different application versions during
the platform's ongoing evolution
- Optimized third-party API usage and application architecture, scaling the platform to support 10,000+
concurrent users
- Worked directly with stakeholders across time zones, translating product requirements into technical
solutions and contributing to architecture and implementation decisions

- Collaborated within an Agile/Scrum team, participating in technical discussions, code reviews, and
iterative delivery
- Supported team knowledge sharing and onboarding, helping engineers understand the evolving
microservice architecture, shared UI components, and development practices

Technology Stack
React, React Native, Nest.js, Node.js, Express.js, Sequelize, TypeORM, GraphQL, Apollo, Storybook, Next.js, Jest,
Docker, AWS

| AI-powered content creation platform
(the name is under NDA)

Description
This platform utilizes AI technology to help small businesses simplify their creative workflow and reduce
investments in content services. Its features include product photo generation, copywriting support, logo design,
icon creation, and content editing. The app provides a free version with limited features and a paid version with
extensive credits and export options.

Responsibilities
- Leading the technical delivery of AI-powered product capabilities, translating high-level business
requirements into scalable technical solutions
- Refining and architecting solutions from top-level product requirements, balancing functionality,
maintainability, performance, and implementation complexity
- Architecting and developing a custom graphic editor for product photo generation, content editing, logo
creation, icons, and other creative workflows
- Designing and integrating AI-powered workflows with OpenAI for automated copywriting, image
generation, and AI-assisted design capabilities
- Leading full-stack feature development across Next.js and Firebase, owning functionality from frontend
implementation through backend integration
- Refactoring and optimizing the application architecture to improve maintainability, performance, and the
platform's ability to evolve as new capabilities were introduced
- Designing and implementing automated testing, including unit and end-to-end tests to maintain
reliability and regression coverage
- Architecting third-party integrations including Stripe for payments and Algolia for content search

Technology Stack
Next.js, Firebase, Jotai, Img.ly, MaterialUI, OpenAI, Stripe, Algolia

| Weather forecasting app
(the name is under NDA)

Description
This application provides quick and easy tracking of weather conditions in different cities. It is designed to work
on both web and mobile platforms, providing a seamless user experience that simplifies navigation and

managing weather cards. This means you can access a comprehensive weather forecast anytime, on any
device.

Responsibilities
- Architected and led the development of the application from scratch, translating high-level product
requirements into a modular, scalable solution for web and mobile
- Designed the overall system architecture to support shared business logic and consistent user
experiences across multiple platforms
- Designed and implemented secure authentication and role-based authorization to protect user and
application data
- Architected third-party API integrations for real-time weather forecasting across multiple locations
- Designed and implemented Redis caching strategies to improve API response times, reduce
unnecessary external API calls, and ensure reliable application performance
- Led frontend development with React, Redux, and Material UI, building responsive interfaces and
reusable application components
- Designed backend architecture and data models using NestJS, TypeORM, and PostgreSQL, establishing
clear separation between application layers and data access
- Containerized the application with Docker, ensuring consistent development, testing, and deployment
environments
- Defined and documented key technical decisions, architecture, and development workflows to support
maintainability and future team onboarding

Technology Stack
TypeScript, React, Redux, MaterialUi, React Hook Form, Yup, Axios, NestJS, TypeORM, PostgreSQL, Redis,
Docker

| Platform for FOXOPTICA: optics retail business
Description
A full-featured web application designed for an optics retail business, allowing users to browse and purchase
glasses online, book eye exams, and locate nearby physical stores. The platform supports both customer-facing
and admin-facing functionality, ensuring a seamless omnichannel shopping experience. The goal was to digitize
and automate key retail workflows, enabling the business to scale its services while improving user engagement
and operational efficiency.

Responsibilities
- Owned the product and technical delivery of the platform, translating business needs from an optics
retail operation into a scalable digital solution
- Led development from concept to production, designing and implementing both frontend and backend
functionality from scratch
- Architected a modular application structure to support long-term scalability, maintainability, and
expansion of the retail business
- Designed and implemented secure authentication and role-based authorization across customer and
administrative workflows
- Architected e-commerce workflows including product catalog, order placement, checkout, payments,
and appointment scheduling

- Designed and implemented an admin platform for managing inventory, orders, customers, and
day-to-day business operations
- Integrated payment functionality to support secure online transactions
- Established smoke and integration testing to maintain reliability across critical customer and operational
workflows
- Owned the platform post-launch, driving technical improvements, maintenance, updates, and product
iterations based on direct customer and business feedback
- Made product and technical decisions based on direct business ownership, continuously identifying
opportunities to digitize and automate operational workflows

Technology Stack
TypeScript, React, Redux, Express

| Platform for Gravis: building company specializing in stretch ceilings
Description
A web application for a building company specializing in stretch ceilings. The platform allows users to learn
about the company's services, calculate pricing for custom stretch ceilings, and place orders directly for both
manufacturing and installation. The website aims to streamline the customer journey from discovery to purchase,
improving the overall user experience and increasing conversions.

Responsibilities
- Owned the product and technical development of the platform, translating the company's business
processes into a digital customer and ordering experience
- Led end-to-end development from scratch, covering architecture, frontend, backend, integrations,
deployment, and ongoing maintenance
- Architected and evolved the application for scalability, maintainability, and future business growth
- Designed user flows and prepared wireframes/mockups, connecting business requirements with
practical customer journeys before implementation
- Designed and implemented a custom pricing workflow that allowed customers to calculate the cost of
bespoke stretch ceilings and submit orders for manufacturing and installation
- Built the full customer journey across frontend and backend, from service discovery and pricing through
order submission
- Integrated payment gateways and order management workflows to support the company's sales and
fulfillment processes
- Led performance optimization and post-launch improvements, maintaining system stability while
continuously refining the product based on real customer feedback
- Made product and technical decisions as the business owner, using direct knowledge of operations and
customers to prioritize functionality and improve the digital sales process

Technology Stack
JQuery, HTML, PHP, MySQL