Денис

DENYS SAPONKO
Middle Node.js Backend Engineer
Mykolayiv, Ukraine [відкрити контакти](див. вище в блоці «контактна інформація») [відкрити контакти](див. вище в блоці «контактна інформація»)

PROFILE
Middle Node.js Backend Engineer with 3.5+ years of commercial experience building and maintaining backend
applications and microservices. Experienced in database and query optimization, caching, asynchronous processing,
legacy system modernization, automated testing, CI/CD and backend reliability. Worked in international product and
outsourcing teams.

TECHNICAL SKILLS
Backend Node.js, TypeScript, JavaScript, NestJS, Express, Fastify, REST APIs
Databases PostgreSQL, MongoDB, SQL, Complex Queries, Transactions, Indexing, Query Optimization,
Migrations
Messaging & Cache RabbitMQ, Redis
Architecture Microservices, asynchronous and HTTP service communication
DevOps & Cloud Docker, Docker Compose, Kubernetes, CI/CD Pipelines, Docker Image Builds, AWS S3
Quality & Reliability Unit/E2E Testing, Health Checks, Rate Limiting, Logging
Monitoring Prometheus, Grafana
AI / LLM Gemini API Integration, Function Calling, Structured Outputs, Embeddings, RAG with pgvector

PROFESSIONAL EXPERIENCE
Middle Software Engineer - Brainstack | Oct 2024 - Mar 2026
Searqle
Worked on a US-focused platform for searching publicly available information about individuals, including public
records related to legal history, debts, violations and other available records. The backend collected and processed
information from multiple external public data sources based on user-provided search data.
Developed and maintained services using Node.js, TypeScript, Fastify and NestJS. PostgreSQL was the primary
relational database, while MongoDB was used for document-oriented data with flexible JSON-like structures. Worked
beyond basic ORM operations with complex SQL and UNION queries, transactions, migrations and indexes.
Optimized slow database operations by restructuring queries, adjusting indexes and database structures, and
moving frequently accessed data to Redis.
Used Redis for user sessions, authentication-related data and frequently requested database data. Used RabbitMQ
for asynchronous transfer of reports and payment-related information between services. Implemented API-level rate
limiting and health checks covering the backend, PostgreSQL, Redis and RabbitMQ, allowing unavailable
components to be detected and recovery procedures to be triggered.
Worked with Docker-based development environments and CI/CD pipelines, including creating pipelines from
scratch, adding stages/jobs, configuring Docker image builds, running tests and linting before deployment, and
deploying applications across development, staging and production environments. Used existing
Prometheus/Grafana monitoring after deployments and performed basic Kubernetes operational tasks such as
checking pods and service availability. Wrote unit/E2E tests and participated in code reviews and production issue
investigation.
Middle Software Engineer - SoftServe | Oct 2021 - Sep 2023
Mining Operations Platform
Worked on a production platform for collecting and processing mining operations data using Node.js, TypeScript and
Express. Developed backend functionality and maintained existing services, using PostgreSQL as the primary
relational store and MongoDB for data that did not require a strict relational structure.
Worked with complex SQL, transactions and database structures rather than relying exclusively on ORM-level
operations. Used Redis to cache large datasets assembled from multiple database tables, reducing repeated
expensive queries and improving response times for frequently requested data. Several backend services
communicated directly over HTTP where synchronous communication was sufficient.
Worked with Docker/Docker Compose, Kubernetes and AWS S3 as part of the development environment and
application infrastructure. Wrote unit and E2E tests for important business functionality and participated in code
reviews and technical discussions.
Car Number Tracker
Worked on modernization of a vehicle tracking platform consisting of several legacy JavaScript backend projects.
After the product was approved for further development, the team modernized its technical foundation before
expanding the platform.
Migrated the existing backend projects from JavaScript to TypeScript and NestJS, restructuring them as independent
services within a microservice architecture. Implemented RabbitMQ communication between services and adapted
existing business logic and database functionality to the new architecture while preserving original system behavior.

After the core migration, stabilized the services, resolved issues discovered during the transition, added backend
functionality and covered important parts of the migrated system with automated tests. The result was a working
NestJS-based microservice backend prepared for continued product development.
Node.js Software Engineer - dSTAR Lab Ltd | Jun 2020 - Sep 2021
Started as a Junior JavaScript Developer and gradually took on broader backend responsibilities across several
projects. Developed backend business logic and microservices, contributed to application architecture, maintained
existing functionality and wrote automated tests. Participated in code reviews and technical discussions,
collaborated with frontend, QA, DevOps and product teams, mentored trainee developers and temporarily
coordinated development work on one project.

EDUCATION
Master's Degree - Petro Mohyla Black Sea National University | 2020 - 2022
Bachelor of Science - Petro Mohyla Black Sea National University | 2016 - 2020

LANGUAGES
English: B2 / Upper-Intermediate Ukrainian: Native Russian: Fluent