Kostiantyn

Kos antyn Orekhov
Lead Full-Stack Software Engineer

Summary
19+ years of hands-on experience designing and developing scalable web and desktop
applications on the .NET platform.

Proven expertise in system architecture, code refactoring, and performance optimization,
improving application efficiency and maintainability.

Proficient in modern JavaScript frameworks — Angular (JS, 2+), React, NestJS, and
Next.js (SSR) — building responsive, component-driven UIs and full-stack solutions.

Strong background in database architecture and query optimization across MS SQL,
PostgreSQL, MongoDB, and Redis, ensuring high-performance data access and
reliability.

Deep understanding of asynchronous programming models (TAP, Reactive Extensions,
DataFlow, CSP) for high-concurrency systems.

Experienced with Node.js, gRPC, RabbitMQ, CQRS, and Event Sourcing, designing
event-driven microservice architectures.

Skilled in Agile/SCRUM delivery, unit/integration testing, and code review practices,
fostering collaboration and continuous improvement.

Adept at mentoring teams, conducting technical interviews, and driving architectural
decisions aligned with business goals.

Tech Stack
Backend:
.NET (Framework & Core 3–9) – development of scalable backend services and APIs
C#, ASP.NET MVC, Web API – RESTful architecture, middleware, and business logic
implementation
Entity Framework/Core, Dapper, NHibernate, ADO.NET – ORM and high-
performance data access layers

Frontend:
Angular (1.x–14), React, TypeScript – building responsive, SPA and SSR frontends
Angular Material, jQuery – UI components and legacy system support
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Cloud & Integrations:
AWS (Kubernetes, Lambda, S3) – containerized deployment and serverless processing
Azure (Event Hub, Cosmos DB, Functions, Blob, Search Index, Table Storage) – cloud
data processing and distributed services
RabbitMQ, gRPC – asynchronous, event-driven microservice communication
Hangfire, Redis, MongoDB, Cosmos DB, Docker – background jobs, caching, NoSQL
and containerized environments

Testing & Quality:
xUnit, Jest, Selenium, Telerik Reporting, Microsoft Fakes – unit, integration, UI, and
report testing automation

DevOps & Tools:
Kubernetes, Argo CD, Git, Jira, Visual Studio, Rider – CI/CD, version control, task
tracking, and IDE workflow

Selected Work Experience

CQL agency — Senior Back-End Developer

Dec 2025 – Now

• Designed and developed MarketingHub, an event-driven integration
platform for transactional email and SMS processing between enterprise
commerce systems and Bloomreach Engagement.

• Implemented scalable microservice architecture using .NET, Azure
Functions, Azure Service Bus, and RabbitMQ for high-volume
asynchronous event processing.

• Built integrations with OrderGroove, OMS, Shopify, and Bloomreach
APIs, including secure HMAC/API key authentication and payload
transformation pipelines.

• Developed configurable template mapping and routing mechanisms for
transactional notifications, supporting dynamic business rules and multi-
channel delivery workflows.

• Improved platform reliability by implementing deduplication strategies, retry
policies, distributed tracing, structured logging, and observability using
OpenTelemetry and Application Insights.

• Optimized system performance and resiliency for external API integrations by
introducing retry/fallback mechanisms, stale-cache recovery, and enhanced
error handling for high-load scenarios.

• Collaborated closely with distributed US teams, participating in architecture
 discussions, code reviews, production troubleshooting, and mentoring
engineers.

Technologies: NET 9/10, C#, ASP.NET Core, Azure Functions, Azure Service Bus,
Docker, Azure DevOps, OpenTelemetry, Application Insights, AccountDb, Bloomreach,
Shopify, REST APIs

Toppan Security — Senior Full-Stack Developer

May 2025 – Nov 2025

• Led development of the Ethiopian Service Portal, a national-scale ID and
Passport management system used by multiple government agencies.

• Designed and provisioned a Kubernetes cluster on AWS, enabling scalable
microservice deployment and GitOps workflows via Argo CD.

• Integrated Vault for secret management and MinIO with S3 compatibility for
secure document and media storage.

• Refactored and maintained legacy .NET services, migrating critical components
toward modern architectures (.NET 9, REST/gRPC).

• Implemented Node.js (NestJS, Express) microservices with Jest unit testing to
improve reliability and maintainability.

Technologies: .NET 9, C#, Node.js, NestJS, Express, AWS, Kubernetes, Argo CD, Vault,
MinIO (S3), PostgreSQL, Jest

LondonLink — Senior Full-Stack Developer

Jul 2023 – Feb 2025

Designed and developed new trading and portfolio management features for a high-load
financial platform serving thousands of concurrent users.

• Modernized and refactored legacy .NET 4.7–8.0 backend modules to improve
performance, scalability, and maintainability.

• Implemented real-time communication between services using RabbitMQ and
gRPC, ensuring reliable data flow across distributed components.

• Collaborated with cross-functional teams to deliver React-based front-end
 updates aligned with UX and business requirements.

• Deployed and monitored services on AWS, optimizing CI/CD pipelines and
system observability.

Technologies: .NET 4.7–8.0, C#, Node.js, React, AWS, RabbitMQ, gRPC, PostgreSQL

Playtika — Senior Back-End Developer

Sep 2022 – Apr 2023

• Developed and deployed new game features for Caesars Slots, one of Playtika’s
top-grossing social casino games with millions of active users.

• Integrated new game assets and optimized backend logic to improve feature
stability and loading performance.

• Collaborated with front-end and QA teams to ensure smooth rollout of updates
across multiple environments.

• Supported migration from .NET Framework 4.7 to .NET Core 3.0, enhancing
scalability and maintainability of game services.

Technologies: .NET Framework 4.7 – Core 3.0, C#, Rider, Private Cloud, REST APIs

Dzinf Finance — Senior Back-End Developer

Sep 2021 – May 2022

• Designed and implemented custom white-label banking modules for multiple
fintech clients, enabling rapid onboarding and configuration of new partners.
 • Enhanced and refactored the admin panel (Angular + .NET Core) to improve
usability, performance, and security.

• Integrated AWS services for cloud deployment and data storage, and optimized
PostgreSQL queries for transaction-heavy workloads.

• Collaborated closely with front-end and QA teams to ensure stability and
compliance with financial requirements.

Technologies: .NET Core 3.0–6.0, C#, Angular, AWS, PostgreSQL, REST APIs

EPAM (Refinitiv) — Senior Back-End Developer

Dec 2020 – May 2021

• Developed and optimized financial data processing modules for Refinitiv, a
leading global provider of financial market data and analytics.

• Implemented real-time analysis features for trading insights and reporting
dashboards.

• Improved system performance and stability, reducing response time and API
latency.

• Collaborated with distributed teams across multiple time zones following Agile/
SCRUM methodology.

Technologies: .NET (Core), C#, AWS (Lambda, S3, EC2), REST APIs

Paragonex — Senior Full-Stack Developer

Dec 2019 – Jul 2020

• Re-engineered a legacy trading platform, migrating from outdated web
technologies to a modern React + .NET Web API architecture.

• Designed and implemented real-time data streaming using WebSockets,
improving user experience and system responsiveness.

• Collaborated with UI/UX and backend teams to align new functionality with
business requirements and trading workflows.
 • Optimized database interactions and ensured smooth integration with Oracle-
based financial data systems.

Technologies: .NET Framework, C#, React, Oracle, WebSockets, REST APIs
Educa7on
Tavrida National University — M.Sc. in Mathematics and Computer Science
Graduated: 1990-1995

Contacts
Phone: [відкрити контакти](див. вище в блоці «контактна інформація»)

Telegram: @BetterThanOther

Email: [відкрити контакти](див. вище в блоці «контактна інформація»)