Krzysztof Onishi

Senior Software Engineer at CAZOO

Developed backend systems for a high-traffic e-commerce platform supporting 2M+ monthly users, improving transaction throughput and payment reliability. Led PSP migration, redesigning workflows with Java 17, Spring Boot, Hibernate, reducing latency by 25% and improving fault tolerance. Built custom tools for automated dispute resolution, boosting internal efficiency by 40%. Designed microservices with REST APIs, asynchronous messaging, and caching for high availability. Implemented AI-assisted components for payment anomaly detection and workflow optimization, improving error handling by 30%. Implemented cloud monitoring/observability with AWS CloudWatch and ELK, reducing incident response times by 30%. Mentored junior engineers, led architecture reviews, and ensured adherence to best practices.

Software Engineer at Luxoft

Delivered enterprise backend solutions for fintech and e-commerce platforms with 1M+ daily active users, ensuring performance, security, and scalability. Modernized Rakuten Europe legacy systems by migrating monoliths to Spring Boot microservices with event-driven Kafka, improving uptime by 35%. Implemented multi-PSP payment flows with PCI-DSS compliance, reducing transaction failures by 20%. Built custom integration tools for customer support, payment dispute resolution, and automated workflows, increasing efficiency by 35%. Optimized databases (PostgreSQL, Cassandra, Oracle) and contributed to CI/CD pipelines with Jenkins, Docker, Kubernetes. Worked with cross-functional teams and integrated Python/JavaScript components for AI-assisted analytics and automated reporting.

Software Engineer at Rakuten

Developed global e-commerce backend systems processing millions of transactions daily across currencies. Built RESTful and SOAP APIs for payment, order management, and vendor integration using Java EE and Spring MVC. Refactored legacy components with design patterns, reducing technical debt by 30%. Developed internal tools for payments and loyalty programs, improving resolution times by 25%. Optimized database queries (Oracle, PostgreSQL) and implemented Python/JavaScript scripts for AI-based anomaly detection and reporting dashboards.

Senior Software Engineer at CAZOO

Led backend development for a high-traffic e-commerce platform serving 2M+ monthly users. Spearheaded the PSP migration, redesigned workflows with Java 17, Spring Boot, and Hibernate, reducing latency by 25% and boosting fault tolerance. Built custom tools for automated dispute resolution, improving internal efficiency by 40%. Designed a microservices architecture with REST APIs, asynchronous messaging, and caching for high availability. Introduced BDD testing with Cucumber and JUnit 5 and automated CI/CD pipelines using Maven, Docker, and GitHub Actions. Implemented AI-enabled service components for payment anomaly detection and workflow optimization, improving error handling by 30%. Integrated cloud monitoring with AWS CloudWatch and ELK, reducing incident response times by 30%. Mentored junior engineers and led architecture reviews.

Software Engineer at Luxoft

Delivered enterprise backend solutions for fintech and e-commerce with 1M+ daily active users. Modernized Rakuten Europe legacy systems by migrating monoliths to Spring Boot microservices with Kafka-based event-driven architecture, improving uptime by 35%. Implemented multi-PSP payment flows with PCI-DSS compliance, reducing transaction failures by 20%. Built custom integration tools for customer support, payment dispute resolution, and automated workflows, increasing efficiency by 35%. Optimized databases (PostgreSQL, Cassandra, Oracle) for high-traffic scenarios. Developed CI/CD pipelines with Jenkins, Docker, and Kubernetes for faster, reliable deployments. Collaborated across teams on design patterns and modular architecture. Integrated Python and JavaScript components for AI-assisted analytics and automated reporting.

Software Engineer at Rakuten

Developed global e-commerce backend processing millions of transactions daily across multiple currencies. Built RESTful and SOAP APIs for payments, order management, and vendor integration using Java EE and Spring MVC. Refactored legacy components with design patterns (Factory, Observer, Singleton), reducing technical debt by ~30%. Created internal tools for payments and loyalty programs, improving resolution times by ~25%. Optimized database queries with Oracle and PostgreSQL and implemented Python/JavaScript scripts for automated data processing, AI-based anomaly detection, and reporting dashboards.

Senior Software Engineer at CAZOO

Developed backend for a high-traffic e-commerce platform serving 2M+ monthly users; Led PSP migration, redesigned payment workflows, reducing latency by 25% and improving fault tolerance; Built custom tools for automated dispute resolution; Designed microservices with REST APIs, asynchronous messaging, and caching; Introduced BDD testing and automated CI/CD; Implemented AI-assisted service components for payment anomaly detection and workflow optimization; Implemented cloud monitoring/observability; Mentored junior engineers and led architecture reviews.

Software Engineer at Luxoft

Delivered enterprise backend solutions for fintech and e-commerce platforms with 1M+ daily active users; Modernized Rakuten Europe legacy systems by migrating monoliths to Spring Boot microservices with event-driven architecture (Kafka); Implemented multi-PSP payment flows with PCI-DSS compliance; Built custom integration tools for customer support, payment dispute resolution, and automated workflows; Optimized databases (PostgreSQL, Cassandra, Oracle); Developed CI/CD pipelines with Jenkins, Docker, Kubernetes; Collaborated with cross-functional teams on design patterns and modular architecture; Integrated Python and JavaScript components for AI-assisted analytics and automated reporting.

Software Engineer at Rakuten

Developed global e-commerce backend systems processing millions of transactions daily across multiple currencies; Built RESTful and SOAP APIs for payment, order management, and vendor integration; Refactored legacy components reducing technical debt by 30%; Developed internal tools for payments and loyalty programs; Optimized database queries for peak loads; Wrote Python and JavaScript scripts for automated data processing and AI-based anomaly detection.

Senior Software Engineer at CAZOO

Led backend development for a high-traffic e-commerce platform serving 2M+ monthly users, improving transaction throughput and payment reliability. Migrated PSP workflows using Java 17, Spring Boot, and Hibernate to reduce latency by 25% and enhance fault tolerance. Built automated dispute resolution tools, boosting efficiency by 40%. Designed microservices with REST, asynchronous messaging, and caching for high availability. Introduced BDD testing (Cucumber, JUnit 5) and CI/CD pipelines (Maven, Docker, GitHub Actions). Implemented AI-assisted components for payment anomaly detection and workflow optimization, improving error handling by 30%. Integrated AWS CloudWatch and ELK for observability, cutting incident response times by 30%. Mentored juniors and led architecture reviews, promoting best practices.

Software Engineer at Luxoft

Delivered enterprise backend solutions for fintech and e-commerce platforms with 1M+ daily active users, ensuring performance, security and scalability. Modernized Rakuten Europe legacy systems by migrating monoliths to Spring Boot microservices with Kafka-based event-driven architecture, improving uptime by 35%. Implemented multi-PSP payment flows with PCI-DSS compliance, reducing transaction failures by 20%. Built custom integration tools for customer support, payment disputes, and automated workflows, increasing efficiency by 35%. Optimized databases (PostgreSQL, Cassandra, Oracle) to improve query performance under high load. Developed CI/CD pipelines with Jenkins, Docker, Kubernetes, enabling faster, reliable deployments. Collaborated on design patterns and modular architecture, improving maintainability. Integrated Python and JavaScript components for AI-assisted analytics and automated reporting, boosting operational intelligence.