# Orest Klymko

> Orest Klymko is a software architect and senior backend engineer based in Bratislava, Slovakia, working remotely with US and EU product teams in Kotlin, Java, Spring Boot, Kafka and Kubernetes. He designs, builds, audits and optimizes distributed systems end to end on B2B contracts, with clients in the United States, Slovakia, Czechia, Austria, the rest of the EU and Ukraine.

- Name: Orest Klymko (Ukrainian: Орест Климко)
- Role: Software Architect, Senior Backend Engineer, Tech Lead
- Location: Bratislava, Slovakia (remote, EU and US hours)
- Languages: Ukrainian (native), Slovak (C1), Russian (C1), English (professional working proficiency)
- Current: Software Architect & Tech Lead at DATALAN (since May 2026); Co-Founder & Software Architect of MMA Finds (since 2024)
- Previously: Software Engineer at Erste Digital (Erste Group, Austria's largest banking group), Backend & Full-stack Developer at GAMO a.s., Backend Developer at Nestify
- Education: Bachelor of Engineering, Technical University of Košice
- Engagement: B2B through an EU-registered company, or via Deel, Remote.com or Oyster; invoiced monthly in EUR or USD
- Contact: orest.klymko2020@gmail.com · +421 902 655 237 · booking: https://calendar.google.com/calendar/appointments/schedules/AcZssZ3l4vj4_v2gKXHISEfXTQoRN8tcwfOfOREtN9JsaTyqcZYY_FnqqMIle5EHeEDS-JdDE_op5oZr?gv=true
- Profiles: https://linkedin.com/in/orest-klymko · https://github.com/OrestKlymko
- Site languages: English https://orest-klymko.dev/ · Slovak https://orest-klymko.dev/sk/ · Czech https://orest-klymko.dev/cs/ · Ukrainian https://orest-klymko.dev/uk/

## Services

- Systems built end to end: From business requirements to production operations. I have designed and shipped systems of different complexity for different business niches: banking, enterprise data and linked-data platforms, request management, a consumer mobile product. Backend, web, iOS and Android apps, infrastructure and monitoring, with one accountable person for all of it.
- Architecture and performance audits: A measured picture of where the system is slow, fragile or expensive, and a prioritized plan to fix it. Benchmarks on realistic data before anything touches production, so decisions rest on numbers rather than guesses.
- Backend delivery for agencies and teams: Kotlin and Java on Spring Boot, PostgreSQL, Kafka, Kubernetes. I plug into an existing team as a senior backend engineer or lead the backend of a client project on your behalf, with API standards, reviews and CI/CD included.
- Optimization of existing systems: Slow queries, stuck background jobs, incidents nobody can trace. I make running systems fast, observable and reliable, shipped in stages so the business gets value early, and usually without new infrastructure or licenses.

## Engagements

- Backend performance & reliability audit (Fixed scope · 2 weeks): I go through the code, the data and the production metrics and hand over a written report: where the system is slow, fragile or expensive, what that costs the business, and a prioritized fix plan. Ends with a walkthrough call with your team.
- Fractional architect (Monthly · a few hours a week): Senior architecture on your team without a full-time hire: design and architecture reviews, review of critical-path pull requests and a regular call with the CTO or tech lead.
- Senior backend contractor (Full-time or part-time): Kotlin or Java on Spring Boot, PostgreSQL, Kafka and Kubernetes, inside your team. B2B through my EU-registered company or via Deel, Remote.com or Oyster.
- Scope and price are agreed after a 30-minute call, once I understand the system and the problem. Audit details: https://orest-klymko.dev/audit/

## Verified production results

- Filtered search over 25–50 million records: from 30+ minutes to under one second; worst-case substring search from ~80 s to ~1 ms, with no new infrastructure or licenses.
- Crash-safe asynchronous export pipeline: 300,000-record multi-format exports with no loss, no duplicates and automatic recovery.
- Observability from zero: one trace ID across a 7-service chain including RabbitMQ and Apache NiFi, shipped as a shared library.
- MMA Finds (https://www.mmafinds.com): a vertical marketplace for the MMA industry designed and built solo — Java / Spring Boot 3, PostgreSQL, Kafka, Keycloak, Stripe, FCM, React Native on iOS and Android, Docker and Nginx on Hetzner. Thousands of users; absorbed 700 registrations in three hours on a single day.

## Skills

- Languages & frameworks: Kotlin, Java 17 / 21, Spring Boot, Spring Security, Spring Data, Hibernate, JUnit, Mockito
- Architecture: Microservices, Event-driven, DDD, REST API design, API gateway, Blue-green releases
- Data & messaging: PostgreSQL, MongoDB, Oracle, Redis, Kafka, RabbitMQ, Apache NiFi
- Semantic web & linked data: RDF, RDF4J, SPARQL, OWL / ontologies, Triple stores, Linked data publishing
- Infrastructure & observability: Kubernetes, Docker, Helm, ArgoCD, GitOps, CI/CD, OpenTelemetry, Grafana, Tempo, Loki, Prometheus
- Security: Keycloak, OAuth2 / OIDC, JWT, Spring Security
- Deployment: Kubernetes, Docker, Helm, ArgoCD, GitOps, Hetzner, VPS / bare metal, Nginx, TLS
- Mobile release: iOS · App Store, Android · Google Play, React Native, Code signing, OTA updates
- CI/CD: GitLab CI, GitHub Actions, Jenkins, Automated tests, Liquibase / Flyway
- Monitoring & alerting: Grafana, Prometheus, Loki, Tempo, OpenTelemetry, Alerting
- Messaging & data infrastructure: Kafka, RabbitMQ, Apache NiFi, PostgreSQL, MongoDB, Redis

## Experience

- May 2026 — present — Software Architect & Tech Lead, DATALAN (Bratislava · Remote): Own end-to-end architecture of an enterprise data pipeline platform: NiFi, Kafka, RabbitMQ, MongoDB, PostgreSQL and Spring Boot microservices on Kubernetes. Translate business requirements into service boundaries and integration contracts, implement critical paths, own GitOps deployments with ArgoCD, built the observability stack and the team-wide API standards (RFC 7807).
- 2025 — 2026 — Software Engineer, Erste Digital (Vienna · Hybrid): Austria’s largest banking group, 15M+ customers. Owned projects end to end across 10+ microservices, designed REST APIs and third-party integrations, led architecture reviews in the backend team, introduced blue-green zero-downtime releases and optimized CI/CD.
- 2024 — present — Co-Founder & Software Architect, MMA Finds (Slovakia · Remote): Sole architect and engineer of a vertical marketplace for the MMA industry: Java / Spring Boot 3 backend on PostgreSQL and Kafka, React Native app on iOS and Android, Keycloak OIDC with PKCE, Stripe payments and in-app credits, FCM notifications, messaging and rewards. Docker, Nginx and Hetzner infrastructure, store releases and production operations included.
- 2024 — 2025 — Backend & Full-stack Developer, GAMO a.s. (Banská Bystrica · Hybrid): Java and Kotlin microservices on Spring Boot for enterprise request and data management. Optimized Oracle queries for high-frequency workloads, built REST APIs and Angular components, integration tests, Liquibase schema versioning.
- 2021 — 2024 — Backend Developer, Nestify (Bratislava · Remote): REST APIs on Spring Boot, Java, Kotlin and PostgreSQL. Event-driven microservices, Flyway migrations, Next.js server-rendered features delivered alongside frontend and QA teams.

## Case studies

- [Designing and shipping a two-sided marketplace as its only engineer](https://orest-klymko.dev/work/mma-finds-marketplace/): One engineer, every layer. Live on iOS and Android with thousands of users; absorbed 700 registrations in three hours on a single day.
- [A job that can crash, retry, or run twice — and still never lose an order](https://orest-klymko.dev/work/async-publish-pipeline/): A 300,000-record, multi-format export moved out of the request thread entirely — and made impossible to lose, duplicate, or leave stuck forever.
- [From "grep every pod and hope" to one trace ID across a 7-service chain](https://orest-klymko.dev/work/observability-from-zero/): From guessing which of seven services (plus NiFi, twice) swallowed a record, to pasting one ID and watching its whole journey unfold.
- [Cut filtered dataset search from 30+ minutes to sub-second at 25–50M records](https://orest-klymko.dev/work/dataset-search-at-scale/): 30+ min → sub-second filtered search; worst-case substring search 80s → ~1ms; flat to 50M records; zero new infrastructure, no new license

## FAQ

### Who is Orest Klymko?
Orest Klymko is a software architect and senior backend engineer based in Bratislava, Slovakia. He works remotely with US and EU product teams in Kotlin, Java, Spring Boot, Kafka and Kubernetes, and has shipped production systems at Erste Digital, DATALAN and his own marketplace, MMA Finds.

### What can Orest Klymko build or fix for my company?
Orest designs and builds backend systems end to end, audits architecture and performance, joins agency or product teams as a senior backend engineer, and optimizes slow or unreliable production systems. He also ships web, iOS and Android apps when a project needs them.

### Which countries does Orest Klymko work with?
Orest is based in Bratislava and works remotely with clients in Slovakia, Czechia, Austria, the rest of the European Union, Ukraine and the United States. Core hours overlap with US Eastern time from 9:00 to 13:00.

### Can I hire Orest Klymko on a B2B contract?
Yes. Orest contracts through his EU-registered company (B2B) or via Deel, Remote.com or Oyster, invoiced monthly in EUR or USD. No visa sponsorship is required. Engagements can be full-time, part-time, fixed-scope or fractional architecture.

### What technology stack does Orest Klymko use?
Backend: Kotlin, Java 17/21, Spring Boot, PostgreSQL, MongoDB, Oracle, Redis, Kafka, RabbitMQ and Apache NiFi. Infrastructure: Kubernetes, Docker, Helm, ArgoCD, Hetzner, Nginx, OpenTelemetry and Grafana. Frontend and mobile: TypeScript, React, React Native, Angular and Next.js.

### What results has Orest Klymko delivered in production?
Filtered search over 25–50 million records went from 30+ minutes to under a second. A crash-safe pipeline exports 300,000 records without loss or duplication. One trace ID now follows a request across 7 services. None of it needed new infrastructure or licenses.

### Which industries has Orest Klymko worked in?
Banking at Erste Digital, Austria’s largest banking group with 15M+ customers; enterprise data and linked-data platforms at DATALAN; enterprise request management at GAMO; SaaS backends at Nestify; and a consumer sports marketplace, MMA Finds, which he co-founded.

### Which languages does Orest Klymko speak?
Orest speaks Ukrainian natively, Slovak and Russian at C1 level, and English at a professional working level. Czech clients work with him in Slovak, which is mutually intelligible with Czech. Technical documentation and code reviews are written in English.

### How do I start working with Orest Klymko?
Book a 30-minute Google Meet call through the calendar on this page or send an email to orest.klymko2020@gmail.com. The first call covers the business problem, the current system and the fastest safe path to a result.

## Optional

- [About](https://orest-klymko.dev/about/): full CV
- [Contact](https://orest-klymko.dev/contact/)
- [CV (PDF)](https://orest-klymko.dev/Orest_Klymko_Resume.pdf)