Олександр

Oleksandr Bunin
Senior Java Engineer | Spring, Legacy Modernization
[open contact info](look above in the "contact info" section) | [open contact info](look above in the "contact info" section) | Kyiv | [open contact info](look above in the "contact info" section)

Summary
Senior Java Engineer with 8+ years building production-grade, high-concurrency SaaS on the Spring stack,
specializing in modernizing legacy systems without stopping the business. Led a legacy monolith to microservices to
Spring Modulith evolution using the Strangler Fig pattern, migrated a platform from Java 11 to Java 25, and
replaced dual writes with a Kafka Transactional Outbox across a 20+ service ecosystem serving 500+ tenants. Works
across Spring Boot, Spring Security, Spring Data JPA, Spring Cloud, and Spring Kafka, with some Scala in
production, running on Kubernetes and AWS. Ran an observability and resiliency program with the ELK stack,
Jaeger, and Resilience4j that cut MTTR roughly 60%. Comfortable owning architecture end to end and defining
engineering standards for a team.

Technical Skills
Java & JVM: Java 8–25, Scala, Hibernate/JPA, JUnit 5, Mockito, Testcontainers, ArchUnit, Maven, Gradle
Spring: Spring Boot, Spring Modulith, Spring Security, Spring Data JPA, Spring Cloud (Gateway, OpenFeign,
Config), Spring Kafka, Spring Batch
Legacy Modernization: Monolith to Microservices, Strangler Fig, Modular Monolith, Java Version Upgrades,
Transactional Outbox, Incremental Data Migration, Flyway
Kubernetes & Cloud: Kubernetes, Helm, Docker, AWS (EC2, EKS, RDS, S3, CloudFront, Route 53), SAP BTP,
Cloud Foundry
Observability: ELK Stack (Elasticsearch, Logstash, Kibana), Jaeger, Micrometer, Prometheus, Grafana, Resilience4j
Data & Messaging: PostgreSQL, Redis, Kafka, SAP HANA Cloud, SAP Event Mesh, Protocol Buffers
Architecture: Microservices, DDD, Event-Driven Systems, Multi-Tenant SaaS, REST, gRPC, WebSockets, OAuth2,
OIDC, JWT
Also: Python, FastAPI, Golang, React, TypeScript, LangChain, LangGraph

Professional Experience
06/2024 – Present Senior Java Engineer
Remote LeverX International LLC
High-performance internal SaaS used daily by SAP Account Executive teams worldwide to
model enterprise deals across TCV, ACV, LEP, and IT1 and IT2 calculations over multi-
year, multi-product scenarios.
Led the platform's evolution from a legacy monolith to microservices to Spring
Modulith, using the Strangler Fig pattern to migrate incrementally with no downtime,
and cutting p95 latency by replacing HTTP and Event Mesh calls with in-process events.
Migrated the platform from Java 11 to Java 25 and upgraded Spring Boot and
dependencies, adopting records, sealed types, pattern matching, and virtual threads to
improve performance and maintainability.
Enforced DDD aggregates and module boundaries with Spring Modulith and
ArchUnit tests, so the modular structure could not erode at compile and test time.
Secured the services with Spring Security, OAuth2, and JWT, and built data access
with Spring Data JPA and Hibernate, with schema changes versioned in Flyway.
Built real-time multi-user collaboration over WebSockets with SAP Event Mesh and
optimistic concurrency control, and led the React and TypeScript UI.
Designed an immutable snapshot store for every deal change, serialized with Protocol
Buffers and structural sharing, paired with a domain event log for audit and analytics.
Added resiliency with Resilience4j circuit breakers and idempotent retries with backoff
to stop cascading failures when upstream SAP systems degraded.
Cut MTTR by roughly 60% over a year with structured logging in the ELK stack, Jaeger
tracing, Micrometer metrics, and customer-impact-tuned alerting.

03/2024 – 06/2024 Senior Software Engineer, 3-Month Contract
Remote Promtheon
AI SaaS platform aggregating 40+ LLM, image, and video models into a single agentic
workspace.
Led the Golang orchestration layer routing requests across 40+ model providers behind
a unified API, isolating per-provider failures so one degraded upstream could not stall
unrelated requests.
Built backend APIs and agent workflows in Python, FastAPI, and LangGraph with
Redis-backed caching and SSE streaming.
Drove delivery on AWS with EC2, RDS PostgreSQL, S3, CloudFront, and Route 53,
with Docker-based deploys.

04/2018 – 03/2024 Senior Backend Engineer
Remote LeverX International LLC
Multi-tenant SaaS on AWS dispatching work to tens of thousands of field technicians
across 500+ customer tenants.
Developed features across a 20+ microservice ecosystem on Java and Spring Boot, with
Spring Cloud Gateway and OpenFeign for routing and service calls and Spring
Cloud Config for centralized configuration, keeping strict tenant isolation.
Replaced dual writes with Kafka event flows using the Transactional Outbox pattern
and Spring Kafka, eliminating inconsistencies that caused divergent state between
services during the move off the legacy dispatching core.
Built Spring Batch jobs for bulk tenant data imports and nightly reconciliation, and
migrated data incrementally from legacy schemas.
Developed and maintained Scala services for event processing alongside the Java
microservices.
Ran the services on Kubernetes with Helm charts on AWS EKS, with Prometheus
and Grafana dashboards and centralized logs in ELK.
Cut dynamic plugin compilation latency by roughly 90% through response compression
and caching of compiled artifacts.
Optimized PostgreSQL queries and indexing to raise throughput during peak
dispatching volume.
Sustained roughly 90% test coverage with JUnit 5, Mockito, and Testcontainers
integration tests, gating production deployments.

Education
09/2024 – 02/2026 Master's Degree, Computer Software Engineering
Open International University of Human Development "Ukraine"
09/2016 – 06/2020 Bachelor of Science in Applied Mathematics
Kyiv Polytechnic Institute, Physical-Technical Institute