Senior Kotlin/Java Backend Engineer for Fintech Payments

SMARTCORE AG; Barcelona; Presencial; EUR 90.000 - 130.000; Jornada completa

Ventajas ofrecidas por este puesto de trabajo

Competitive salary

Modern technology stack

Training budget and conference support

Corporate access to top-tier LLMs

Descripción de la vacante

SmartCore is a fintech holding building infrastructure for the next generation of payments. You’ll join a key team responsible for developing and evolving our core acquiring platform — a high-load, microservices-based system operating 24/7, handling the entire payment lifecycle with PCI DSS compliance.

You’ll design and implement new microservices in Kotlin/Java, optimize performance, and contribute to architecture decisions to boost fault tolerance, scalability and security.

Formación

• Has at least 10 years of commercial backend development experience with Java/Kotlin.
• Demonstrates expert-level proficiency in Kotlin: idioms, coroutines, functional features, and applies them effectively.
• Deep knowledge of Java Core and the JVM ecosystem.
• Has excellent command of Spring Boot — REST APIs, internals, auto-configuration, Spring Security, and Actuator.
• Expert in PostgreSQL — designing complex data schemas, optimizing queries, replication mechanisms.
• Experience with MongoDB.
• Hands-on experience building systems with Kafka — producer/consumer patterns, delivery guarantees.
• Familiar with RabbitMQ and Redis (caching, pub/sub, distributed locks).
• Experience designing distributed, fault-tolerant systems (microservices, CQRS, Event Sourcing).
• Comfortable with modern AI technologies, including AI agents and LLMs.
• Understanding of networking protocols (TCP/IP, HTTP/2, gRPC).
• Experience with Docker and Kubernetes.
• Writes clean, maintainable, and well-tested code.
• Highly autonomous, proactive, and takes full ownership of product quality and outcomes.
• Fluent in Russian (B2 or higher) — required for daily communication within the team.

Responsabilidades

• Design and develop new microservices and business logic using Kotlin and Java.
• Optimize the performance of existing system components and handle high-load areas of the codebase.
• Make key architectural decisions aimed at improving fault tolerance, scalability, and platform security.
• Integrate with third-party payment systems, banks, and processing centers.
• Work with asynchronous data streams using Kafka and RabbitMQ.
• Conduct code reviews, mentor less experienced colleagues, and promote best development practices.
• Actively participate in R&D — exploring and integrating new technologies into the project stack.
• Write unit and integration tests to maintain a high-quality codebase.

Conocimientos

Java

Kotlin

Spring Boot

PostgreSQL

MongoDB

Kafka

RabbitMQ

Redis

Microservices

CQRS

Event Sourcing

AI integration

gRPC

Docker

Kubernetes

Unit testing

Herramientas

Docker

Kubernetes

Prometheus

Grafana

Jaeger

Descripción del empleo

SmartCore is a fintech holding building infrastructure for the next generation of payments. You’ll join a key team responsible for developing and evolving our core acquiring platform — a high-load, microservices-based system operating 24/7, handling the entire payment lifecycle with PCI DSS compliance.

You’ll design and implement new microservices in Kotlin/Java, optimize performance, and contribute to architecture decisions to boost fault tolerance, scalability and security.