Piotr Frelik

With a strong love for coding honed over years of practice, I enjoy building teams, writing clean code, and solving challenges with modern technology. I always think carefully before making decisions, focusing on creating flexible and maintainable solutions. While I value good coding practices like DDD, TDD, and SOLID principles, I know that delivering projects on time is crucial for business success. I'm eager to learn and stay updated with the latest trends to contribute effectively to your goals.

.Net Developer, ING Tech Europe (Amsterdam, Netherlands)                                                                     April 2024 - Present

• Optimized the integration of the Temenos solution with the Transaction Handler API, achieving a 20% reduction in authentication processing times, resulting in a more seamless user experience.
• Migrated legacy Web Forms applications to ASP.NET Core or MVC, enhancing performance and security
• Emphasizes modernization efforts, such as moving from old technologies to new frameworks, which improves maintainability and supports business goals without disrupting operations.
• Developed and maintained RESTful APIs using C#, ASP.NET Web API to facilitate communication between frontend and backend systems.
• Integrated third-party APIs and services, such as payment gateways and geolocation services, to extend application functionality and provide value-added features.
• Developed and maintained messaging systems using RabbitMQ, enabling seamless communication between microservices in distributed architectures.
• Implemented automated testing strategies using NUnit and Moq frameworks to validate application behavior and ensure robustness.
• Involves integrating components to optimize performance in transaction-heavy environments, such as POS systems across retail locations, ensuring seamless and efficient transaction processing.
• Designed and implemented microservices architectures using .NET Core, improving modularity and allowing for independent deployment and scaling of services.
• Established strong vendor relationships and streamlined integration processes, reducing integration time by 30% and increasing system interoperability with external banking systems by 20%.
• Employed continuous integration (CI) and continuous deployment (CD) pipelines using Jenkins or Azure DevOps to automate build, test, and deployment processes.
• Participated in Agile development methodologies such as Scrum, attending daily stand-ups, sprint planning, and retrospective meetings to drive project progress and ensure alignment with business goals.
• Utilized MuleSoft for API integration, ensuring seamless data flow and interoperability between the Temenos solution and other banking systems, enhancing overall system efficiency.
• Completed a thorough review of existing documentation on Confluence, identifying areas that require updates or clarifications.
• Integrated Octopus Deploy with Azure DevOps and Jenkins to automate the release process, ensuring consistency and eliminating manual intervention.
• Set up SQL Server Agent jobs to automate the execution of SSIS packages, ensuring timely and consistent data processing. 
• Led the migration of outdated Web Forms applications to modern platforms like ASP.NET Core or MVC, ensuring continuity of business operations while enhancing application performance, security, and maintainability.
• Started organizing and structuring the documentation for the Legacy Web API, ensuring it aligns with current practices and is user-friendly.
• Collaborated with relevant stakeholders to gather missing information and confirm technical details, resulting in more comprehensive documentation.
• Expertly handled models, variables, and message flows within Mulesoft, ensuring smooth data transformations and seamless integration across systems.
• Facilitated team collaboration and documentation using Confluence, fostering a culture of continuous improvement and customer service.
• Automated test cases and implemented unit tests for cloud front applications, ensuring high-quality production support.
• Ensured that all API documentation is easily accessible and up-to-date in the related systems, facilitating user onboarding and support.
• Actively contributed to knowledge sharing initiatives, documenting technical solutions, and creating internal training materials to empower team members and foster a culture of learning and growth.
• Worked closely with QA and DevOps teams to ensure the smooth rollout of new features and updates via Octopus Deploy, enhancing the overall deployment lifecycle efficiency.

Lead .NET Full Stack Developer, Capgemini Engineering (Kraków, Poland)                       January 2022 – February 2024

• Led the development of a comprehensive web application for internal use, integrating all company modules to streamline operations and enhance productivity.
• Created a web application for internal use, encompassing all modules utilized within the company.
• Developed and maintained a robust e-commerce platform using ASP.NET Core and Entity Framework, facilitating a seamless shopping experience for users and increasing online sales by 25% within the first year of launch.
• Integrated payment gateways and third-party services, such as PayPal and Stripe, ensuring secure and efficient transaction processing while enhancing user trust and satisfaction.
• Implemented features like product search, user authentication, and shopping cart functionalities, leveraging design patterns to ensure scalability and maintainability of the codebase.
• Experience includes improving transaction processing speeds and implementing security protocols like OAuth and JWT
• Implemented NuGet package versioning strategies to ensure backward compatibility and seamless updates across dependent projects.
• Managed legacy systems utilizing Entity Framework 6, optimizing existing queries and enhancing performance through indexing strategies, resulting in a 30% reduction in database access times.
• Conducted code reviews and refactoring sessions to transition legacy code to a more maintainable architecture while integrating new features, thereby increasing overall system reliability.
• Designed and implemented ETL packages using SSIS to automate data integration workflows and improve data quality.
• Utilized third-party libraries like EasyNetQ to simplify RabbitMQ integration, improving message queuing and routing efficiency.
• Implemented RESTful APIs in MVC applications to support seamless data exchange between client-side applications and back-end services. Implemented RESTful APIs in MVC applications to support seamless data exchange between client-side applications and back-end services.
• Developed and maintained RESTful APIs using C#, ASP.NET Web API to facilitate communication between frontend and backend systems.
• Designed and implemented features using React JS, C#, ASP.NET, and SQL server.
• Spearheaded the adoption of modern frontend frameworks such as Angular 14 and React, leveraging their component-based architectures to deliver dynamic and responsive user interfaces for web applications
• Implemented Hangfire, ActiveBatch for job scheduling and workload automation, increasing operational efficiency and streamlining business processes.
• Mentored junior developers on best practices and coding standards, improving overall team productivity and code quality.
• Integrated MuleSoft solutions for efficient API management, enhancing connectivity and data integration across various systems, improving overall system interoperability.
• Integrated Azure Application Insights into applications for real-time monitoring and diagnostics, enabling proactive performance optimization and incident resolution
• Implemented Azure New Relic for application performance monitoring, enabling proactive identification of performance issues and real-time optimization.
• Effectively coded in C# .NET using .NET 4.5 techniques like lazy loading, reflection etc
• Integrated NuGet package publishing into CI/CD pipelines using Azure DevOps, automating the deployment process and ensuring timely delivery of updates.
• Applied CI/CD pipelines with Azure and Harness for C# .NET backend and Angular 14 frontend projects, ensuring smooth and efficient deployment processes.
• Optimized application performance by identifying and resolving bottlenecks, conducting profiling and performance tuning using tools like JetBrains dotTrace or Visual Studio Performance Profiler

.NET Full Stack Developer, Allegro Group (Poznań, Poland)                           February 2019 – December 2021

• Designed and developed high-performance and scalable backend payment systems using C# on the .NET platform with Harness, improving transaction processing speeds.
• Collaborated with cross-functional teams such as Product, Design, and QA to ensure timely delivery of features, contributing to project success.
• Developed and maintained complex SSIS packages for data extraction, transformation, and loading (ETL) processes.
• Leveraged Power BI and Datadog for data visualization and monitoring, providing actionable insights to inform business models and improve content management strategies
• Improved performance with Next, TypeScript, Redux, React Hooks, HOC, skilled Object handling.
• Managed state globally with customized hooks, Redux-thunk, slice, Redux-toolkit, Context API.
• Utilized containerization technologies such as Docker and Terraform to enhance scalability and efficiency in product development processes, driving innovation and improving time-to-market.
• Integrated .NET components to optimize POS system performance, ensuring seamless functionality across multiple retail locations.
• Implemented logging, monitoring, and error handling mechanisms using tools like Serilog, ELK Stack (Elasticsearch, Logstash, Kibana), or Application Insights to track application health and diagnose issues.
• Implemented automatic NuGet package restoration in build processes, ensuring smooth and consistent builds across different environments.
• Utilized the .NET framework to develop and maintain Point of Sale (POS) software, enhancing transaction processing and inventory management capabilities.
• Implemented EF, Harness, Hangfire Object/relational-mapping (ORM) solutions, POS techniques for mapping data representation from MVC model to Oracle relational data model with a SQL-based schema.
• Used MongoDB as a persistent store and Apache Kafka as a messaging layer for custom solutions, ensuring data reliability and real-time processing.
• Acted as a liaison between technical and non-technical stakeholders, translating business requirements into technical specifications and providing status updates on project progress and milestones
• Applied design patterns and SOLID principles to develop maintainable and scalable applications, improving overall code quality.

.NET Software Developer, Siemens Digital Industries (Munich, Germany)                                     November 2015 – January 2019

• Architected and developed APIs using .NET Core, providing scalable and maintainable solutions for various applications..
• Implemented authentication and authorization mechanisms using OAuth and JWT tokens to ensure secure access to resources
• Constructed an E-Commerce System and collaborated with 10+ other team members to establish a smooth delivery process, ensuring project success.
• Worked on the development of an extensive ERP system, developing four main plugins (POS, Inventory, Sales, CRM) and enhancing the performance of the CSV files importing module by 30% utilizing a recursive algorithm approach.
• Created a Time and Budgeting system for a large construction company utilizing ASP.NET Core, SQL Server, and C#, improving project tracking and resource management.
• Collaborated with marketing and design teams to create promotional campaigns and A/B testing strategies, leading to a 15% increase in conversion rates during seasonal sales.
• Setting up and administering Kubernetes on Azure with Containers
• Collaborated with cross-functional teams to gather requirements and deliver robust solutions, ensuring alignment with business goals.
• Utilized Azure services and SQL Server for backend development, providing scalable and secure data storage solutions.
• Developed and maintained comprehensive documentation for legacy applications, ensuring that team members could effectively navigate and support aging systems while planning for modernization initiatives.
• Implemented Angular Router for navigating between views and lazy-loading modules to optimize performance.
• Enhanced application performance through code optimization and efficient database interactions, resulting in improved user experience.
• Utilized state management libraries such as NgRx in Angular to manage complex application states efficiently.
• Collaborated with UX/UI designers to implement responsive and visually appealing user interfaces using HTML, CSS, and JavaScript frameworks like Angular 5 or React.

Master’s degree, Computer Science                                                                      October 2015

Jagiellonian University (Kraków)