Denys

Senior Java Backend Engineer - High-Load Systems, Big Data
& AI

Location: Ukraine | Remote
Email: [відкрити контакти](див. вище в блоці «контактна інформація») | Phone: [відкрити контакти](див. вище в блоці «контактна інформація»)

PROFESSIONAL SUMMARY

Senior Java Backend Engineer with 10+ years of experience delivering mission-critical, high-load
distributed systems and enterprise platforms. Proven expertise in designing scalable microservices
architectures, event-driven platforms, payment processing systems, and cloud-native solutions. Strong
background in FinTech, cybersecurity, insurance, gaming, telecom, and transportation industries. Actively
integrating AI/LLM technologies, RAG pipelines, MCP-based model orchestration, and vector databases
into production systems to automate workflows, improve knowledge retrieval, and enhance customer
experience.

CORE TECHNICAL SKILLS

Languages: Java (10+ years), Python, Go, JavaScript
Backend: Spring Boot, Spring Framework, Spring MVC, Spring WebFlux, REST APIs, Microservices,
Apache Camel
Distributed Systems & Messaging: Apache Kafka, RabbitMQ, AWS SQS, AWS SNS
Databases & Storage: PostgreSQL, Oracle, MongoDB, Cassandra, Elasticsearch, Solr, Vector Databases
Cloud & DevOps: AWS (Lambda, Big Data services), Docker, Kubernetes, CI/CD, WildFly, Maven, Git
Data & Big Data: Apache Spark
Security: OAuth 2.0, JWT Authentication, PCI compliance, SSL
AI & ML: LLM integration, AI Agents, MCP Model Integration, RAG pipelines, Embeddings, Semantic
Search
Monitoring & Observability: Grafana, ELK Stack
Testing: JUnit
Architecture & Engineering: High-load systems, multithreading, system design, SOLID principles, design
patterns
Frontend & Others: React, RxJava, Liquibase

PROFESSIONAL EXPERIENCE

Senior Software Engineer / Senior Java Developer (Current)
• Architecting and scaling microservices platforms for enterprise insurance systems (policy, claims, billing,
integrations).
• Designing Kafka-based event-driven architectures processing millions of events daily.
• Leading backend system design, reliability improvements, and performance optimization initiatives.
• Mentoring engineers, conducting architectural reviews, and enforcing clean-code standards.
• Integrating AI/LLM-powered services (chatbots, document analysis, workflow automation).
• Designing and deploying RAG pipelines backed by vector databases for enterprise knowledge search.
• Implementing MCP-based model orchestration for multi-agent workflows and tool execution.

Tech: Java, Spring Boot, Kafka, PostgreSQL, Docker, Kubernetes, AWS, Vector DB, LLM APIs, MCP
FinTech - Electronic Payment Processing Systems
• Designed and implemented large-scale payment gateways processing Mastercard, Visa, and American
Express transactions.
• Built complete transaction lifecycle: EMV, authorization, clearing, settlement, reconciliation.
• Implemented ISO-8583 and BER-TLV protocols with high-availability routing and failover strategies.
• Integrated with GlobalPayments, FirstData, SIX, Omnipay, AMEX, Lufthansa, and multiple EU/US banks.
• Developed fraud detection mechanisms using rule-based logic and ML-assisted models.

Tech: Java, Spring Boot, PostgreSQL, Redis, AWS

Cybersecurity SaaS Platform
• Developed backend services for vulnerability scanning, malware detection, SSL/PCI compliance, and
phishing protection.
• Built high-throughput asynchronous processing pipelines optimized for AWS cloud infrastructure.

Tech: Java, Spring Boot, Kafka, MongoDB, Elasticsearch, AWS

High-Load Gaming Platforms
• Developed backend infrastructure for online gaming platforms with 200k+ concurrent users.
• Optimized system performance, latency, and scalability under peak load conditions.

Tech: Java, Spring, Redis, PostgreSQL, Kafka

Social Network Platform
• Designed scalable multi-tier backend architecture for high-traffic social networking services.
• Participated in content ranking and recommendation system experiments.

Tech: Java, Spring Boot, PostgreSQL, Elasticsearch

Telecom & Transportation Systems (KPN, Dutch Railways)
• Built geolocation and tracking services using GSM/CellID/GPS data sources.
• Developed SOAP and REST services and PostgreSQL/PostGIS clustering solutions.
• Worked on traffic routing and route optimization algorithms.

Tech: Java EE, SOAP/REST, PostgreSQL, PostGIS

ADDITIONAL INFORMATION & EXPERTISE

AI Architecture & RAG Systems:
• Design and implementation of Retrieval-Augmented Generation (RAG) pipelines for enterprise document
search and customer support automation.
• Experience with vector databases for semantic search and embeddings storage.
• Integration of LLM providers (OpenAI-compatible APIs) for chatbots, summarization, and knowledge
assistants.
• MCP (Model Context Protocol) integration for multi-agent orchestration, tool calling, and secure model
access.

High-Load & Scalability:
• Architecture of horizontally scalable backend services handling hundreds of thousands of concurrent
users.
• Design of fault-tolerant systems with automatic failover, retry strategies, and circuit breakers.
• Performance tuning, JVM optimization, garbage collection tuning, and database query optimization.

Security & Compliance:
• PCI DSS aligned system design for payment processing platforms.
• OAuth2/JWT-based authentication and authorization for microservices ecosystems.
• Secure API design and data protection practices.

Leadership & Collaboration:
• Technical mentoring of mid and senior engineers.
• Architecture reviews and system design interviews.
• Collaboration with product managers, data scientists, and DevOps teams in distributed environments.

EDUCATION

Bachelor’s / Master’s Degree in Computer Science

LANGUAGES

English - Upper-Intermediate (B2)