Senior Kotlin/Java Backend Engineer – Fintech Payments

SMARTCORE AG; Barcelona; Presencial; EUR 90.000 - 150.000; Jornada completa

Ventajas ofrecidas por este puesto de trabajo

Competitive salary

Modern tech stack

Training budget & conferences

Access to top-tier LLMs

Descripción de la vacante

SmartCore AG is building a scalable core acquiring platform for a fast-growing fintech. You will design and implement microservices in Kotlin/Java, focusing on high performance, fault tolerance, and security. You will work with Kafka/RabbitMQ, PostgreSQL, MongoDB, and modern containers in a distributed team.

The role requires deep JVM, Spring Boot expertise, and strong problem-solving skills. You will mentor peers, participate in R&D and ensure high-quality code with tests, while collaborating

Formación

• 10+ years of backend development experience with Java/Kotlin.
• Expert in Kotlin idioms, coroutines, functional features and practical use.
• Deep knowledge of Java Core and the JVM ecosystem.
• Excellent command of Spring Boot including REST APIs, auto-configuration, Spring Security and Actuator.
• Expert in PostgreSQL: complex schemas, query optimization, isolation levels and replication.
• Experience with MongoDB.
• Hands-on experience with Kafka (brokers, producers/consumers, delivery guarantees).
• Familiar with RabbitMQ and Redis (caching, pub/sub, distributed locks).
• Experience building distributed, fault-tolerant microservices (CQRS, Event Sourcing).
• Comfortable with AI technologies and applying LLMs in practice.
• Knowledge of networking protocols (TCP/IP, HTTP/2, gRPC).
• Experience with Docker/Kubernetes for containerization/orchestration.
• Writes clean, maintainable, well-tested code.
• Highly autonomous and accountable for product quality.
• Fluent in Russian (B2+).

Responsabilidades

• Design and develop new microservices and business logic using Kotlin and Java.
• Optimize performance of high-load system components and code areas.
• Make architectural decisions to improve fault tolerance, scalability and security.
• Integrate with third-party payment systems, banks, and processing centers.
• Work with asynchronous data streams using Kafka and RabbitMQ.
• Conduct code reviews, mentor colleagues and promote best practices.
• Participate in R&D to evaluate new technologies for the stack.
• Write unit and integration tests to maintain a high-quality codebase.

Conocimientos

Java/Kotlin backend

Kotlin coroutines

Spring Boot

PostgreSQL

MongoDB

Kafka

RabbitMQ

Redis

Microservices architecture

CQRS & Event Sourcing

Docker & Kubernetes

Distributed systems

Russian language

Code quality & tests

AI/LLM integration

Herramientas

Docker

Kubernetes

Kafka

RabbitMQ

Redis

PostgreSQL

MongoDB

Spring Boot

gRPC

Descripción del empleo

SmartCore AG is building a scalable core acquiring platform for a fast-growing fintech. You will design and implement microservices in Kotlin/Java, focusing on high performance, fault tolerance, and security. You will work with Kafka/RabbitMQ, PostgreSQL, MongoDB, and modern containers in a distributed team.

The role requires deep JVM, Spring Boot expertise, and strong problem-solving skills. You will mentor peers, participate in R&D and ensure high-quality code with tests, while collaborating