Systems that hold upunder real load.
Software architect and backend engineer for Kotlin and Java systems that have outgrown their first design. Hands-on in the code, accountable for the architecture above it.
I work remotely with US and EU product teams whose Kotlin or Java backends have become slow, fragile or hard to trace: audits, fractional architecture and senior backend delivery.
30 min → <1 s
filtered search at 25–50M records
15M+
customers at the banking group whose backends I built
700 in 3 h
sign-ups absorbed in a single day at MMA Finds
7 → 1
services traced end to end with one ID
Sound familiar?
The problems teams bring me in for.
Search or reports take minutes
What was fine at 1M rows crawls at 50M. Query-shaped indexes, keyset pagination and measured fixes bring it back to milliseconds.Read how it was solved →Background jobs get stuck or run twice
Exports, syncs and payments that silently hang or double-fire. Leases, recovery and database-level guarantees make them boring.Read how it was solved →Incidents nobody can trace
Seven services, a queue and an integration tool, and every outage starts with grepping pods. One trace ID changes that.Read how it was solved →A launch your stack has to survive
A spike of sign-ups, payments that must not double-charge, notifications that must not block requests.Read how it was solved →Engagements
Three ways to work together.
Fixed scope · 2 weeks
Backend performance & reliability audit
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.
Monthly · a few hours a week
Fractional architect
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.
Full-time or part-time
Senior backend contractor
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.
Case studies
How production problems actually got solved.
Real systems, real numbers, client names removed. Each piece walks through the problem, the options measured, and what shipped.
Filtered dataset search from 30+ minutes to sub-second
Four stacked catalog problems fixed in stages: query-shaped indexes, keyset pagination, on-demand counts and a self-provisioned n-gram index. Worst-case substring search 80 s → ~1 ms. No new infrastructure, no new license.Read →300,000 records · 0 lostReliability · async pipelineA job that can crash, retry or run twice and never lose an order
A 300,000-record multi-format export moved out of the request thread. Leased claims, automatic recovery, duplicate rejection at the database, self-cleaning failures and once-only catch-up after downtime.Read →7 services · 1 trace IDObservability · 7 servicesFrom grepping every pod to one trace ID across the whole chain
OpenTelemetry Collector into Grafana, Tempo, Loki and Prometheus. Trace propagation through RabbitMQ and NiFi, wired once in a shared library so every new service is a dependency and a config block.Read →700 sign-ups in 3 hArchitecture · marketplaceA two-sided marketplace, designed and run by one engineer
Core backend plus a Kafka-driven notification service with 22 scenarios, payments that cannot double-credit, iOS and Android apps.Read →Built from zero
MMA Finds: a vertical marketplace, built by one engineer.
A mobile-first platform for the MMA industry connecting fighters, managers, promotions and their employees. Promotions discover fighters and send fight offers; fighters and their representatives find opportunities, negotiate and build reputation. Discovery, matchmaking, messaging, representation, payments, credits and rewards in one product. I co-founded it and built every layer myself, from the first schema to the apps in the stores. Live on iOS and Android with thousands of users; the platform absorbed a spike of 700 registrations in three hours on a single day.
Domain & matchmaking
Four roles with distinct permissions (fighter, manager, promotion, promotion employee). Fight offers as a first-class domain: public, exclusive and multi-candidate offers with benefits and a full lifecycle. Representation modeled as a real relationship with request and approval workflows, not a name field.
Identity & security
Keycloak with OAuth 2.0 / OIDC and PKCE for the native app; email, Google and Apple sign-in. Spring Security validates JWT on the API. Delegated access for promotion employees without exposing owner operations.
Payments & credits
Stripe PaymentIntent and SetupIntent with saved payment methods and webhooks; service and success fees calculated server-side; in-app credit packs on both stores. A store purchase is granted exactly once per transaction ID, so a retried or replayed request cannot credit twice.
Notifications & engagement
A separate notification service consumes Kafka events: 22 scenario handlers turn offers, documents, deadlines, negotiations and credits into push (Expo / FCM) and email, with a dead-letter topic for failed messages. Offer and private messaging; badges, referral rewards and early-registration bonuses.
Mobile & deep links
React Native (Expo) app on iOS and Android, separate DEV and PROD environments, deep linking (mmafinds:// and links.mmafinds.com) straight into profiles, offers and invitations.
Infrastructure
A core Spring Boot backend, a separate notification service connected over Kafka, and a React analytics dashboard for the business. Docker behind Nginx with TLS on Hetzner, 230 Flyway migrations, Prometheus metrics, Loki logs and a DocuSign e-signature integration.
How I work
I build for the business, not just for the ticket.
Risk before code
I get into how the business actually earns and loses money before designing the system. That is how I spot the failure modes that surface later as lost orders, stuck jobs or downtime, and design them out while it is still cheap.
AI-accelerated delivery
I run agent-driven development workflows: coding agents generate implementation and tests under my architecture, I review every change against the standards I set. Faster delivery for the client, with a senior engineer accountable for what ships.
Experience
May 2026 — present
Bratislava · Remote
Software Architect & Tech Lead · DATALAN
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
Vienna · Hybrid
Software Engineer · Erste Digital
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
Slovakia · Remote
Co-Founder & Software Architect · MMA Finds
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
Banská Bystrica · Hybrid
Backend & Full-stack Developer · GAMO a.s.
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
Bratislava · Remote
Backend Developer · Nestify
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.
Skills
Kotlin and Java on Spring Boot, distributed systems on Kubernetes. Everything below has run in production for banks, enterprise data platforms and a consumer mobile product.
Languages & frameworks
Built and maintained 10+ microservices for Erste Digital, an enterprise data pipeline platform at DATALAN and the full backend of MMA Finds. Team-wide API standards with RFC 7807 error contracts, integration test suites, Liquibase and Flyway schema versioning.
Architecture
Translated business requirements into service boundaries and integration contracts. Led architecture reviews, introduced zero-downtime blue-green deployments in a banking environment, designed an event-driven core with real-time chat and notifications.
Data & messaging
Took filtered search over 25–50M records from 30+ minutes to under a second with query-shaped indexes, keyset pagination and an n-gram index. Designed a crash-safe async pipeline that exports 300,000 records without loss or duplication. Optimized Oracle queries for high-frequency workloads.
Semantic web & linked data
Modeled enterprise datasets as RDF, built publishing pipelines that serialize hundreds of thousands of records into multiple RDF formats, and exposed them through SPARQL endpoints. Ontology design, URI strategy and validation as part of the data platform.
Infrastructure & observability
Own GitOps deployments with ArgoCD. Built an observability stack from zero: one trace ID across 7 services, propagated through RabbitMQ and NiFi, packaged as a shared library so every new service gets it with a dependency and a config block.
Security
Keycloak-based identity for a production platform: OIDC login, JWT-secured APIs, role-based access, third-party integrations behind the gateway.
I take a product all the way to production and keep it there: servers, clusters, pipelines, app stores and the monitoring that tells you something is wrong before your customers do.
Deployment
Deploy backends, web apps and full platforms: Kubernetes with GitOps at enterprise scale, Docker on Hetzner for a startup. Domains, certificates, reverse proxies, backups and zero-downtime blue-green releases in a banking environment.
Mobile release
Shipped a React Native app to both stores end to end: build pipelines, certificates and provisioning, store listings, review process, staged rollouts and over-the-air updates.
CI/CD
Pipelines from commit to production with tests, migrations and environment promotion. Optimized CI/CD at Erste Digital and own the delivery pipeline for a data platform at DATALAN.
Monitoring & alerting
Set up observability from zero: dashboards, log aggregation, distributed tracing across 7 services and alert rules that page on what matters. Packaged as a shared library so every new service gets it for free.
Messaging & data infrastructure
Provision, tune and operate the brokers and databases behind the services: indexes, replication, retention, dead-letter handling, capacity planning against real load.
I ship the product surface when the project needs it, and I read the analytics behind it so the interface and the API are optimized for what users actually do.
Frameworks
Built the MMA Finds mobile app in React Native end to end: auth, real-time chat, live updates, push notifications. Delivered Angular components for enterprise data tools and server-rendered Next.js features at Nestify.
Web & product analytics
Define event models and funnels, wire tracking, then read where users drop, hesitate or wait. That data decides what gets redesigned and which endpoints get optimized first, so the work moves conversion and retention, not only response times.
UI/UX
Turn analytics findings into concrete interface changes: shorter flows, clearer states, faster perceived load. Interfaces designed around the data model so they stay fast at production volumes.
What clients and agencies get beyond the code.
Business understanding
I get into how the business earns and loses money before designing. That is how failure modes that later become lost orders, stuck jobs or downtime get designed out while it is still cheap. Most of my optimizations shipped with no new infrastructure or licenses.
Ownership & delivery
One accountable person from requirements to production. Work shipped in stages so the client gets value early and can stop or redirect at any point.
Communication
Led architecture reviews in a banking backend team, wrote the API standards a whole team follows, explain trade-offs in business terms to non-technical stakeholders. Ukrainian, Slovak, Russian and English.
AI-accelerated workflow
Coding agents implement under my architecture and specs; I review every change against the standards I set. Faster delivery for the client, with a senior engineer accountable for what ships.
FAQ
Questions clients ask before the first call.
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.
Let’s talk about your system.
Full-time or part-time remote. Core hours 9:00–13:00 Eastern guaranteed, with wider US overlap on full-time engagements. Contracted through my EU-registered company (B2B) or via Deel, Remote.com or Oyster. Invoiced monthly in USD or EUR. No visa sponsorship required.
Pick a 30-minute slot in my calendar; a Google Meet link is created automatically and sent to your inbox.
Phone
+421 902 655 237GitHub
github.com/OrestKlymko