Xavier Mas Leszkiewicz

November 2024 — Present

At BlueBerryBytes, I operate globally from Dubai, acting as a stabilizing, scaling, and automating technology partner. My role encompasses architecting scalable solutions, overseeing engineering teams, and ensuring the seamless integration of AI-driven and cloud-native technologies. With expertise in full-stack development, mobile, AI, Big Data, and high-performance backend systems, I design and implement robust infrastructures that power our products.

January 2025 — Present

• Dress Up & House Group: Acting as Fractional CTO, scaling technical infrastructure, systems architecture, and digital strategy. Operating as Fractional CTO, overseeing the technical architecture, and digital transformation initiatives to scale their operations. • Qantara Sports: Acting as Fractional CTO, driving technical strategy, cloud database architecture, and advanced AI integration for the talent acquisition platform. • Dawlati: Serving as the lead technical authority, managing AWS engineering, operations, and leading the strategic vision for their digital platforms.

February 2023 — March 2025

• Developed a cross-platform mobile app (iOS/Android) with offline sync, push notifications, and real-time analytics. Swap Health (Ionic, React, Firebase, Google Cloud). • Integrated Firebase Authentication and Firestore, improving data consistency and security. • Built a custom analytics dashboard, allowing stakeholders to track user engagement. AAA (General Motors Messaging System - Node.js, AWS Lambda, DynamoDB, SQS). • Designed and implemented a serverless architecture, reducing operational costs by 30%. • Built a real-time messaging system using WebSockets and AWS SQS, ensuring high availability. • Implemented a failover mechanism using AWS Step Functions to enhance fault tolerance.

February 2022 — February 2023

Transaction Monitoring Platform & Forensics Crypto App (Java, Python, AWS, SQL, React) • Led the architecture and implementation of a real-time fraud detection system for blockchain transactions. • Developed a data pipeline processing 10M+ crypto transactions daily, improving detection accuracy by 25%. • Integrated Kafka and AWS Lambda to build an event-driven microservices architecture. KYT System • Built a crypto compliance dashboard with dynamic graph visualization using D3.js and React. • Implemented machine learning fraud detection models, reducing false positives by 30%.

February 2021 — March 2022

Telefonica IPTV Data Infrastructure (Python, Java, Kafka, MongoDB, Celery) • Developed an ETL pipeline processing terabytes of video streaming data, reducing processing time from 8 hours to 2 hours. • Implemented Kafka Streams for real-time event processing, improving recommendation accuracy.

June 2019 — February 2021

Facebook Ads Retention Platform (React, Redux, Node.js, Clickhouse, Google Cloud) • Designed and built a scalable microservices architecture handling 100,000+ active users. • Implemented automated A/B testing for ad optimization, increasing ROI by 20%. • Developed a data warehouse solution using Clickhouse for real-time analytics.

January 2018 — June 2019

• Designed and implemented a scalable backend infrastructure to support various Machine Learning models, optimizing data flow and system performance. • Collaborated closely with Data Science teams to deploy real-time predictive models, improving recommendation accuracy and fraud detection. • Developed and optimized high-throughput data pipelines using Kafka, Kubernetes, and Docker, ensuring seamless processing of massive datasets. • Integrated Elasticsearch and Kibana for real-time analytics and monitoring, enhancing system observability and debugging capabilities.

January 2017 — January 2018

• Led the architecture and deployment of ML-driven services in a microservices environment, ensuring high availability and fault tolerance. • Automated CI/CD pipelines using Maven and Kubernetes, reducing deployment time by 50% and improving system reliability. • Developed and optimized high-volume data processing pipelines using Java, SQL, NoSQL (MongoDB), and Maven, ensuring efficient data ingestion and storage. • Designed and implemented a distributed data architecture capable of handling millions of transactions per day. • Led the end-to-end development lifecycle, from architecture design to production deployment, ensuring system reliability and scalability. • Implemented data aggregation and transformation strategies, reducing query execution time by 40% and enhancing reporting accuracy.

April 2015 — January 2017

• Worked in a high-security government environment, managing 250,000+ identities with Single Sign-On (SSO) and identity protection. • Led the migration of legacy applications to a modern identity management system, reducing authentication failures by 30%. • Developed and optimized Java-based security applications, integrating Active Directory, Oracle Identity Manager, and Siteminder (SSO) for seamless authentication. • Automated administrative processes with custom scripts in Oracle Identity Manager and Visual Basic, improving efficiency and reducing manual intervention. • Collaborated with cross-functional teams to ensure secure, scalable identity management across various government platforms.