Yan

Yan Serhiienko | Java Developer
Email: [open contact info](look above in the "contact info" section)
Location: Kyiv, Ukraine
LinkedIn: [open contact info](look above in the "contact info" section)
GitHub: https://github.com/seyan99
Telegram: https://t.me/seyan99

Professional Summary
Backend Developer with 3 years of commercial experience, building and optimizing high-load systems using Java and
Spring Boot. Currently owning core backend functionality of a production CRM. Strong background in performance
optimization, PostgreSQL tuning, production troubleshooting, CI/CD, monitoring and infrastructure development.

Technical Skills
Languages: Java 11, Java 17, SQL
Backend: Spring Boot, Spring MVC, Spring Data JPA, Hibernate, REST APIs, Multithreading / Concurrency, OOP, Design
Patterns, Transactions
Databases & Caching: PostgreSQL, Redis, SQL Query Tuning, Index Optimization
Messaging: Apache Kafka
Testing: JUnit, Mockito, Testcontainers, Playwright, Postman, Jmeter
DevOps & Infrastructure: Docker, Jenkins CI/CD, Kubernetes, Linux, HashiCorp Vault
Monitoring: Prometheus, Grafana
Build & Version Control: Maven, Git, ArgoCD
Methodologies: Agile, Code Review, Mentoring

Professional Experience
Quantum Projects (SaaS Advertisement / Marketing) - Java Developer
October 2023 - Present
Developed and maintained multiple services; Led backend refactoring initiatives.
Participated in splitting core backend into 3 separate services; Collaborated with other devs on services infrustructure
development (20+ services); Initiated refactor of main backend service modular structure into monolithic.
Improved critical backend functionality performance by 10-15x through database and query optimization.
Reduced authentication subsystem load by ~30% by implementing Redis-based caching.
Optimized PostgreSQL queries and indexes for a ~20GB production database.
Developed Slack notification system and statistics dashboards for external API integrations later adopted as a
business features.
Implemented Prometheus and Grafana monitoring.
Improved Jenkins CI/CD pipelines: 25% faster build, optional tests, e2e reliability.
Automated database migration between Kubernetes test environments.
Mentored 2 Junior Developers; Conducted 10+ technical interviews.

Education
GoIT - Java Developer Program (2022 - 2023)
National Aviation University - Industrial and Civil Engineering (2014 - 2020)

Languages
English - B2
Ukrainian - C2