04/22/2026 updated

TB
100 % available

Senior Java Backend Engineer — Cloud-Native & AI Integration

Vojcice, Slovakia
Only remote
Informatik, Technische Universität Košice
Vojcice, Slovakia
Only remote
Informatik, Technische Universität Košice

Profile attachments

Tomáš Bortňák — Lebenslauf.pdf

About me

Senior Java backend engineer, 11+ years. Quarkus, Spring Boot, Kafka, Kubernetes, AWS. Event-driven microservices for banking, telco, transport & automotive. AI integration (GPT-4o, Whisper). Remote-first, CET. Available May 2026. B2B/SZČO.

Java (Programming Language)Amazon Web ServicesHibernateJUnitPython (Programming Language)PostgreSQLLiquibaseApache MavenMockitoSpring BootGitLabGitFastAPIKubernetesApache KafkaDockerJenkinsMicroservices
Senior Java backend engineer with 11 years of experience building cloud-native systems for enterprise clients across banking, telecommunications, public transport, and automotive sectors.

Core strengths:
— Deep expertise in Java, Quarkus, and Spring Boot
— Event-driven microservices with Kafka, deployed on Kubernetes and AWS
— Led a production WildFly → Quarkus migration at Scheidt & Bachmann, improving performance and maintainability across European and North American transport systems
— Banking experience as Senior Backend Engineer at Tatra banka (new internet banking platform, Spring Boot microservices, Kafka-based event messaging, core banking integration)
— Backend architect and tech lead across multiple freelance engagements since 2019

AI integration experience:
— Built a production AI contact center platform integrating OpenAI GPT-4o, Whisper (speech-to-text), ElevenLabs (text-to-speech), and Twilio for real-time voice AI
— Delivered a secure cloud-ready backend for an industrial AI application (BIOGAS plant management) with audit trails, role-based access, multilingual reporting, and Kubernetes deployment

Working style:
— Remote-first, based in CET timezone (Slovakia)
— Strong architecture and technical-leadership background
— Comfortable working independently or as part of distributed teams
— Prior DACH experience including onsite knowledge transfer in Bonn, Germany

Currently finishing a client engagement at the end of April. Fully available from May 2026 for remote DACH projects, 40 hours per week. B2B contracting via Slovak ICO (SZCO). Working hours 09:00–18:00 CET.

Experience

Professional experience10+ years
Freelancer since2019

Languages

GermanGoodEnglishFluentSlovakNative speakerSpanishBasic knowledgeCzechFluent

Project history

Software Engineer / Consultant

Freelance
Selbständige Tätigkeit als Backend-Entwickler und Consultant für verschiedene Projekte und Unternehmen

Backend Developer

Confidential
Designed and delivered a secure, cloud-ready backend for daily plant logs, maintenance records, feedstock and production tracking, and compliance reporting. Modeled core domain entities with strict audit trails and immutable event history. Exposed REST APIs for web and mobile clients, implemented role-based access (admin, operator, auditor) with JWT authentication. Built reporting pipelines (daily/weekly/monthly) with PDF/CSV export. Added integrations for telemetry imports with validation and anomaly checks. Implemented multilingual support (DE/EN) and timezone-safe scheduling. Set up CI/CD, containerization, and observability (health checks, structured logs, metrics, alerts). Technologies: Java, Spring Boot, PostgreSQL, Flyway, JPA, Hibernate, REST, OpenAPI, Docker, Kubernetes, Elasticsearch, MapStruct, Lombok, JUnit 5, Mockito, GitHub Actions

Senior Backend Engineer

Confidential
Designed and developed an AI-powered contact center solution integrating real-time voice communication with conversational AI. Implemented backend services in Java Spring Boot responsible for AI workflow orchestration, user session management, and third-party API integration. Integrated OpenAI GPT-4o for natural language understanding and response generation. Connected Whisper (speech-to-text) and ElevenLabs (text-to-speech) for bidirectional human-AI voice interaction. Developed APIs for Twilio call routing, voice stream processing, and AI response streaming. Designed a modular architecture enabling scalability and extension toward multilingual voice bots. Technologies: Java, Spring Boot, REST APIs, OpenAI GPT-4o, Whisper, ElevenLabs, Twilio, WebSockets, Docker, PostgreSQL, AWS

Senior Backend Engineer

Scheidt & Bachmann
Backend engineering on enterprise solutions supporting public transportation systems for clients across Europe and North America. Led migration from WildFly to Quarkus, improving performance and maintainability across the platform. Developed new features and maintained Spring Boot-based backend services. Implemented persistence layers and database migrations using Hibernate and Flyway. Contributed to performance optimization and system scalability across microservices. Collaborated with architects on solution design. Involved in deployment automation and Kubernetes orchestration. Technologies: Java, Spring Boot, Quarkus, Hibernate, Flyway, PostgreSQL, Kafka, Kubernetes, Docker, CI/CD, GitLab, WildFly

Senior Backend Engineer / Tech Lead

Slovak Telekom
Collaborated with architects to design and implement scalable backend systems for enterprise web applications. Provided technical leadership in developing systems using Java, Spring Boot, Python, and PostgreSQL on AWS. Promoted best practices in CI/CD, code quality, and performance optimization. Acted as a technical escalation point for complex issues. Technologies: Java, Spring Boot, PostgreSQL, Python, AWS, Jenkins, SonarQube, Kubernetes, Kafka

Senior Backend Engineer

Tatra banka
Senior Backend Engineer on a new internet banking application for children. Collaborated with the bank's solution architect on scalable Spring Boot microservices architecture. Designed and implemented the REST API layer and database model, integrating with existing core banking systems. Built reliable Kafka-based messaging for event-driven communication between services. Participated in CI/CD pipeline setup, container orchestration, and deployments on AWS and Kubernetes. Technologies: Java, Spring Boot, Hibernate, Liquibase, PostgreSQL, Kafka, AWS, Kubernetes, Docker, CI/CD (GitLab/Jenkins), REST APIs

Senior Backend Engineer

NESS Košice
Actively participated in architectural discussions to design microservices-based solutions supporting complex sales processes. Ensured alignment of system design with business requirements and enterprise standards. Led the adoption of AWS, Kubernetes, and CI/CD pipelines. Mentored junior developers in Java, Spring, and modern engineering practices. Technologies: Java, Quarkus, Spring Boot, JavaScript, Microservices, AWS, PostgreSQL, Oracle, Hibernate, Liquibase, Kafka

Java Solution Developer

Východoslovenská energetika Holding a.s.
Entwicklung von Anwendungen zur Verwaltung von Stromzahlungen und Netzanschlüssen mit Spring Boot und Hibernate

Application Developer

T-Systems Slovakia s.r.o.
Entwicklung von Webanwendungen und Mobilfunknetz-Management-Systemen mit Java, Angular und REST APIs

Softwareentwickler IT-Abteilung

U-Shin Slovakia s.r.o.
Entwicklung interner Systeme für die Automobilindustrie, Digitalisierung von Werkzeugen und Qualitätsprüfungs-Anwendungen

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