May 19, 2026
Senior Java Backend Engineer
Senior • Hybrid
27,000 - 33,000 PLN
Krakow, Poland
Are you eager to work with advanced technologies and build high-performance applications capable of processing over 5 million requests per second? If yes, we have an ideal opportunity for you at LoopMe.
We are a team of experienced engineers developing and supporting real-time bidding platforms for global advertisers. You will work daily with talented engineers, using technologies such as Java, Spring Boot, gRPC, Project Reactor, Kafka, ClickHouse, PostgreSQL, Aerospike, and Redis. Your main focus will be on enhancing performance, optimizing cloud infrastructure, and developing innovative features across our product range.
Join us in our mission to expand the limits of possibilities in the advertising industry!
We are seeking a Senior Java Backend Engineer to join our Marketplace team and help develop our high-load ad-serving system, which can process more than 5 million requests per second with a 200ms response time.
What you’ll be doing
Designing and tuning hot-path components for the ad-serving critical path—such as throttling, rate limiting, targeting indexes, and DSP adapters.
Implementing architectural changes across services — including RTB request lifecycle, deals targeting, and multi-impression-key processing.
Creating gRPC APIs and Protocol Buffers schemas to facilitate cross-team integrations.
Profiling and minimizing CPU usage and allocations to achieve strict p99 latency goals.
Strengthening the system architecture to guarantee smooth operation during peak load times.
Integrating advanced targeting algorithms into the main ad delivery process.
Collaborating closely with multiple teams to provide services and data for our solutions.
Core qualifications
Over five years of experience in backend engineering.
Solid understanding of Java and Spring / Spring Boot.
Hands-on experience with SQL and familiarity with PostgreSQL or other relational databases.
Strong knowledge of microservices architecture and its best practices.
Proficient in Linux shell and Docker.
Additional experience we’d value
Concurrency in Java includes java.util.concurrent, CompletableFuture, lock-free data structures, virtual threads / Project Loom, and Reactor schedulers.
gRPC and Protocol Buffers
Project Reactor / Spring WebFlux
Kafka
Kubernetes
Experience in managing high-QPS services, including profiling with JFR and async-profiler, GC tuning, and JVM internals understanding.
Robust testing culture with unit tests, functional tests, and Testcontainers.
Extra pluses
AdTech / RTB domain expertise — OpenRTB, DSP/SSP, IVT, deals, cookie-sync, ads.txt, schain
Performance engineering on critical paths — utilizing fastutil / Eclipse Collections, creating allocation-aware code, and optimizing for JIT awareness.
Distributed systems experience includes rate-limiting algorithms such as token bucket, fixed and slidingwindow, as well as back-pressure, circuit breakers, sharding, and consistent hashing.
Observability tools include Micrometer, Prometheus, Grafana, and structured logging.
Full responsibility for managing multi-week epics across multiple teams.
Experience with analytical or in-memory databases such as ClickHouse, Aerospike, Redis.
Benefits
Flexible working schedule with a hybrid type of work
Annual performance bonus
One month of workation (you can work from any part of the world for one month)
Multikafeteria
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Krakow, MA, Poland
120 - 133 PLN
🏢 Summary: Backend role focused on integrating production AI services (LLM APIs, Agentic AI, pipelines) into a Java and Google Cloud Platform ecosystem. The position involves building and optimizing AI-enabled microservices, embedding external AI tools, and ensuring performance, reliability, and scalability in a financial-grade environment. This is not an ML role but a hands-on Java backend position with practical AI integration experience. 🗂️ Requirements: Minimum 5 years commercial experience in Java backend development, Production experience integrating AI tools or Agentic AI (at least one deployed project), Experience building and maintaining microservices, Practical experience with Google Cloud Platform and Vertex AI, Experience integrating and consuming REST APIs, Experience optimizing performance, latency and reliability of services, Experience with LangChain, Ability to design technical architecture for AI-enabled systems 📃 Skills: Java, GCP, VertexAI, LangChain, LangGraph, LLM, REST, Microservices, AgenticAI, RAG, VectorSearch, Kafka, Python, OpenAI, Claude, MCP 🏢 Description: Wspólnie z naszym Partnerem, jedną z największych instytucji finansowych na świecie , poszukujemy doświadczonej osoby na stanowisko Java Backend Engineer/ki specjalizującej się w integracji systemów z narzędziami AI. To nie jest rola ML Engineera ani Data Scientistki – szukamy kogoś z udokumentowanym, produkcyjnym doświadczeniem w osadzaniu usług AI (LLM API, pipeline'y, Agentic AI) w ekosystemie Java i Google Cloud Platform. 💡 TWOJA ROLA: Projektowanie i implementacja modułów integrujących systemy Java z zewnętrznymi serwisami AI (LLM API, Vertex AI i inne). Identyfikacja i eliminacja bottlenecków w działaniu komponentów AI (latency, koszty API, niezawodność). Budowanie i utrzymanie mikroserwisów obsługujących pipeline'y AI w środowisku produkcyjnym GCP. Współpraca z zespołem przy definiowaniu architektury rozwiązań AI-enabled. Aktywne śledzenie nowych narzędzi AI i ocena ich przydatności w projekcie. Dokumentowanie decyzji architektonicznych i wzorców integracyjnych. Code review i wsparcie innych developerów w obszarze integracji AI. Wdrażanie i monitorowanie usług w Google Cloud Platform. 🔎 CZEGO OCZEKUJEMY OD CIEBIE? Min. 5 lat komercyjnego doświadczenia w Java (backend, produkcja) – must have! Udokumentowane, projektowe doświadczenie z narzędziami AI i Agentic AI – min. 1 wdrożony projekt (nie PoC, nie kurs) – must have! Komunikatywność techniczna – praca w środowisku projektowym z kontaktem z zespołem klienta. Samodzielność i proaktywność w środowisku z niedomkniętymi wymaganiami. Praktyczna znajomość Google Cloud Platform (Vertex AI) i LangChain. Lokalizacja: Kraków lub gotowość do pracy zdalnej (do uzgodnienia). Doświadczenie w architekturze mikroserwisowej i pracy z REST API. Mile widziane: RAG, Vector Search, Python, Kafka, Prompt Engineering, MCP, LangGraph, OpenAI GPT, Claude, Event-Driven Architecture. ✨ OFERUJEMY: 🤖 Nowoczesny proces rekrutacji z AI Rekruterem (AIR) - rozmowa 24/7, natychmiastowy feedback, możliwość powtórzenia. Finalną decyzję zawsze podejmuje Rekruter Connectis. Pracę przy budowie produkcyjnych rozwiązań AI w jednej z największych instytucji finansowych na świecie. Nowoczesny stos: Java, GCP, Vertex AI, LangChain, LangGraph, LLM API. Udział w meetupach technologicznych i spotkaniach integracyjnych. 🌍 Praca zdalna z okazjonalnymi wizytami w Krakowie. 5000 PLN za polecenie znajomych do naszych projektów. Wsparcie dedykowanej osoby kontaktowej z Connectis. Stabilna, długofalowa współpraca B2B. Dziękujemy za wszystkie zgłoszenia. Pragniemy poinformować że skontaktujemy się z wybranymi osobami. 12915/OM
Technology
DCV Technologies
Middle Java backend
Mid
Hybrid
Warsaw, Poland
900 - 950 PLN
🏢 Summary: The offer is for a Java Backend Developer role focused on building and maintaining microservices-based systems using Java and Spring technologies. The position involves developing REST APIs, working with containerized applications, and contributing to Agile delivery processes. The role centers on backend engineering, technical design, and collaboration within cross-functional teams. 🗂️ Requirements: Minimum 3+ years professional experience in backend development, Proficiency in Java 8+, Strong experience with Spring Boot and Spring technologies, Experience building microservices, Experience working with REST APIs, Knowledge of HTTPS, SFTP, REST and SOAP protocols, Understanding of microservices architecture and containerization, Experience with Kafka, Experience with Git and GitHub, Experience with Maven and Jenkins, Experience with MySQL and SQL databases, Familiarity with Linux, Experience working in Agile/Scrum environments 📃 Skills: Java, Spring, SpringBoot, REST, Microservices, Kafka, HTTPS, SFTP, SOAP, Linux, Git, GitHub, Maven, Jenkins, Jira, MySQL, SQL, Containerization, Agile 🏢 Description: Job Description: We are looking for skilled Java Backend Developers with strong experience in Java, Spring technologies, and microservices architecture. The ideal candidate will have hands-on expertise in backend development, REST APIs, containerized applications, and Agile delivery environments. Qualifications: Minimum 3+ years of relevant professional experience Proficiency in Java 8+, REST APIs, Spring Boot, and Spring technologies Experience in building microservices and working with Kafka Solid understanding of HTTPS, SFTP, REST API, and SOAP protocols Familiarity with Linux operating systems Strong understanding of microservices architecture and containerization Knowledge of Agile frameworks and principles Experience with Git/GitHub, GitHub Actions, Maven, Jenkins, and Jira Competence with MySQL and SQL databases Strong analytical and problem-solving skills Excellent written and verbal communication skills Ability to collaborate effectively with Product, QA, DevOps, and Agile/Scrum teams Mandatory Skills: Java (Spring) REST APIs Spring Boot and Spring Technologies HTTPS, SFTP, REST API, and SOAP protocols Microservices architecture and containerization Git/GitHub, GitHub Actions, Maven, Jenkins, Jira MySQL and SQL databases Desired Skills: Strong analytical and troubleshooting abilities Excellent communication skills Team collaboration experience within Agile/Scrum environments Roles & Responsibilities: Contribute to technical design and engineering activities Develop strong domain expertise within the project Analyse functional and technical requirements Support architecture and design discussions Collaborate with Architecture and Business teams Participate in development, design, code reviews, and implementation Follow engineering best practices and support continuous improvement initiatives Out of Scope: Creating product requirements Acting as Scrum Master or Product Owner Project Details: Primary focus is on Java backend development.
Technology
N-iX
Senior Java Engineer (#4884)
Senior
Remote
Krakow, Poland
5,800 - 6,100 USD
🏢 Summary: The role involves building and scaling backend services for content discovery, licensing, and delivery platforms using Java and modern backend technologies. You will design RESTful APIs, implement event-driven systems, and model data to support analytics and reporting. The position focuses on clean architecture, scalable systems, and cloud-based deployments within the AWS ecosystem. 🗂️ Requirements: 5+ years backend development experience, Strong proficiency in Java, Experience with Spring Boot and Spring Framework, Experience designing and consuming REST APIs, Experience with Kafka or other streaming platforms, Strong knowledge of relational databases, Ability to write optimized SQL queries, Experience with GraphQL, Exposure to Python or willingness to learn 📃 Skills: Java, Spring, SpringBoot, REST, Kafka, SQL, GraphQL, Python, AWS, Aurora, DynamoDB, DBT, Databricks, Snowflake, Docker, Kubernetes, Node.js, TypeScript 🏢 Description: We're seeking a Software Java Engineer with 5+ years of experience to help build and scale the backend services that power our content discovery, licensing, and delivery platforms across all of our content libraries. You'll join a team that's passionate about clean architecture, performance, and solving complex challenges at scale. If you thrive in a collaborative environment and love building robust APIs, data-driven systems, and data modeling we'd love to hear from you. What You'll Do: Design, implement, and maintain backend services using Java, Spring Boot, and the broader Spring ecosystem. Build and evolve RESTful APIs that power content metadata, search, recommendation, and licensing workflows. Work with Kafka to build event-driven and real-time processing systems. Use SQL and work with relational databases to support structured content metadata. Partner with data and analytics teams to model data in data warehouses, supporting reporting and analytics use cases. Build and maintain DBT models to transform raw data into clean, usable datasets. Leverage the AWS ecosystem for service deployment, data storage, and pipeline orchestration. Contribute to technical discussions, system design, and code reviews. Requirements: 5+ years of professional backend development experience. Strong proficiency in Java, with experience using Spring Boot and Spring Framework. Experience designing and consuming REST APIs. Familiarity with Kafka or other message streaming platforms. Solid understanding of relational databases and writing optimized SQL. Comfortable working with GraphQL. Exposure to Python or willingness to learn. A collaborative mindset with strong communication skills. A passion for clean code, scalable systems, and continuous learning. Nice-to-Have: Practical experience working with data warehouses and DBT for data transformation and modeling. Hands-on experience working with the AWS ecosystem (especially Aurora/Dynamo DB). Experience working with Node.js and/or Typescript. Knowledge of containerization and orchestration (Docker, Kubernetes). Experience with Databricks/Snowflake. Background in building systems for search, metadata enrichment, or digital asset management. We offer: Flexible working format - remote, office-based or flexible A competitive salary and good compensation package Personalized career growth Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more) Active tech communities with regular knowledge sharing Education reimbursement Memorable anniversary presents Corporate events and team buildings Other location-specific benefits