Refactoring Experts in Munich

• Modernization of a large-scale Java enterprise application*

The project is modernizing a complex enterprise application that has grown over many years. The existing Spring-based legacy system runs on Java 8, OSGi, and Eclipse RCP and is being gradually migrated to a modern, maintainable architecture with Java 25 and Quarkus.

Marcus works on analysis, architecture, refactoring, and implementation. One focus is on untangling historically grown structures and dependencies and on building a clean, sustainable Java and Quarkus technology stack.

Tools & technologies: Java 8, Java 25, Quarkus, Hibernate ORM with Panache, EclipseLink, OSGi, Eclipse RCP, Maven, JUnit, Mockito, REST, JSON, Git, Eclipse IDE, IntelliJ IDEA Ultimate, Jira, Confluence

In my role as Senior Cloud DevOps Architect for BP, an oil and gas company, I had the mission to migrate the Electric Vehicle Charging platform of the EV Division from on-premises and Azure to AWS cloud, resulting in a hybrid multi-cloud, multi-tenant SaaS solution.

Deployment with Kubernetes for the application layer meant provisioning Kubernetes clusters managed by EKS and AKS, with a focus on integrating them into a multi-tenant environment. This integration was achieved by using Kubernetes namespaces and access controls to ensure data isolation and privacy enforcement.

In the database layer, we chose an RDS instance with PostgreSQL to support the backend infrastructure of our applications. Tenants shared the same RDS instance, but each had a dedicated schema.

To ingest near real-time data from physical charge points (CPOs), as IoT devices, via the OCPI protocol, we ran into significant delays with batch processing. As a result, we built a real-time streaming data pipeline using Apache Kafka, while prioritizing an event-driven architecture.

Led collaboration across multiple internal teams, external vendors, cloud providers, and on-site partners to integrate over five systems into a unified solution.

Achievements:

• Successfully designed and implemented hybrid multi-cloud solutions, integrating multiple cloud platforms (AWS, Azure) with on-premises infrastructure, using Site-to-Site VPNs, Firewalls, and Load Balancing.
• Led the migration of on-premises infrastructure to multi-cloud, multi-tenant infrastructure, resulting in 30% faster processing times.
• Migrated workloads from VMware and Hyper-V environments to cloud-based VMs, leveraging cloud-native services to optimize performance, cost efficiency, and scalability.
• Designed a multi-tenant Kubernetes platform leveraging the Kubernetes ecosystem, using Karpenter for dynamic EC2 node provisioning, KEDA for event-driven pod autoscaling (e.g., Kafka message lag), and Rancher for centralized monitoring of multiple clusters (EKS, AKS, or on-prem K8s), replacing Microsoft-centric Azure Arc management service.
• Designed and implemented Python-based FastAPI microservices as part of the EV core-backend on AWS EKS application layer, powering data ingestion and customer analytics pipelines.
• Developed asynchronous, event-driven APIs (Python-FastAPI) for real-time integration with CPOs, supporting OCPI 2.3 and OICP protocols.
• Designed and implemented a secure, production-grade Azure Databricks platform using Terraform, ensuring scalability and cost efficiency.
• Migrated on-premises ERP to a hybrid Dynamics 365 architecture with ERP hosted locally and CRM running in Azure, integrated via Azure Arc.
• Automated CI/CD pipelines for Databricks notebooks and jobs using GitHub Actions & Databricks CLI, reducing deployment time. Reduced infrastructure provisioning time by 70% by automating cloud resource deployment with GitOps.
• Ensured compliance with internal audit and data governance standards (GDPR) through OAuth2/OIDC-based authentication and fine-grained role-based access controls.
• Developed a Zero Trust security model, enforcing least-privilege access and microsegmentation, enhancing security posture and compliance with GDPR and NIST.
• Built interactive analytics dashboards in Amazon QuickSight, integrating data from S3 and Redshift to deliver real-time business insights and visualizations with embedded access for multi-tenant users.
• Led cloud security assessments and full-lifecycle cybersecurity integration during M&A, covering AWS, Azure, IAM (Entra ID), and data protection, while aligning security posture with NIST, ISO 27001, and GDPR across hybrid and cloud-native environments.
• Reduced cloud costs by 64% for a client's dev environment by implementing automated start/stop schedules for EC2 and RDS instances via AWS CDK with EventBridge Scheduler or AWS Systems Manager.

Tech stack:

• Infrastructure as Code: Terraform, AWS CDK, Ansible.
• Containers: Kubernetes on EKS, AKS, Docker.
• Streaming Data Processing: Kafka to Confluent Cloud, after AWS MSK.
• Frontend: TypeScript, React, NextJS, Hooks, Styled Components.
• Backend: Python with FastAPI, also Node.js with NestJS.
• Database: Aurora on PostgreSQL with TypeORM, RDS on SQL Server, Azure Databricks full setup and administration, ETL Pipelines.
• CI/CD and GitOps: GitHub Actions, Azure DevOps, ArgoCD.
• Monitoring and Observability: Prometheus and Grafana.
• Virtualization: Hyper-V, VMware Cloud on AWS, Azure Migrate.
• ERP Systems: Odoo, Microsoft Dynamics 365 Business Central on Azure, integrated with Azure Arc.
• Networking: Site-to-Site VPNs, AWS Direct Connect, Azure ExpressRoute, Firewalls (AWS Network Firewall, Azure Firewall).
• Security: IAM, NIST Framework, Zero Trust Security, AWS WAF, AWS Shield, GuardDuty.

Tasks

• Further development of a new ERP system with Blazor
• Generation of e-invoices in the XRechnung and Zugferd formats
• UI/UX design Client-server system
• Windows 11 Technology
• Microsoft .NET 9, Git, Azure DevOps, ASP.NET, MSSQL, Blazor Programming languages
• C#, MVVM Development tools
• Microsoft Visual Studio .NET 2022 Database
• MSSQL Industry
• Other

• Delivered backend systems, data processing solutions, and software integrations for enterprise business applications.
• Designed and implemented API-based services connecting internal platforms with external systems.
• Built automated processing workflows to handle large-scale structured business data.
• Improved application performance by 30–50% through database optimization, caching strategies, and backend refactoring.
• Reduced manual operational effort by 40–60% by automating repetitive workflows.
• Supported production environments through troubleshooting, monitoring improvements, and continuous optimization.
• Authored technical documentation and led knowledge-transfer sessions to support long-term maintainability.

• Designed and implemented end-to-end data pipelines (batch & streaming) using Python, SQL, and Apache Spark, Databricks on AWS reducing ETL latency by 40%.
• Developed serverless event-driven ingestion pipelines using AWS Lambda and SQS, ensuring real-time data availability for downstream analytics.
• Leveraged Google Cloud Platform (GCP) services including BigQuery and Dataflow to manage cross-cloud data warehousing and analytics integration.
• Expertise in DMS (CDC, Full Load) and Airflow for scalable data pipeline automation and orchestration.
• Managed and customized data pipelines using Databricks, Airflow. Automation using Docker, Kubernetes, Terraform.
• Automated data quality checks using dbt to modularize transformations and ensure production-grade data lineage, improving reliability by 30%.
• Collaborated with compliance teams to ensure GDPR and SOC2 alignment. Mentored junior engineers and contributed to architecture refactoring for scalability.
• Created and maintained dashboards in Power BI to provide actionable insights.

• Spring Boot Software Engineer
• DevOps Engineer (Kubernetes, Azure DevOps)

Toolstack: Java, Spring Boot, Kubernetes, Helm, GitOps, ArgoCD, Docker, Azure DevOps, CI/CD Pipelines, Git, Postgres

• Development of the digital organ donation register, commissioned by the Federal Institute for Drugs and Medical Devices (BfArM)

• Implementation of user stories in several microservices (frontend and backend)

• Ensuring quality with unit, integration, and E2E tests

• Conducting code reviews

• Coordination with other development teams

• Taking over the software license check and simplifying the process

• Responsibility for implementing and documenting the business logging

• Setting up a development environment with Docker Compose

• Technologies: TypeScript, JavaScript, Java, HTML, SCSS, JSON, REST, Angular, Nx, NgRx, RxJs, Git, Spring, TFS, Jenkins, Jest, Cypress, UI/UX-Design, Figma, Storybook, Domain-Driven Design (DDD), Micro Frontend, Clean Code, Arc42, Agile, Scrum, Jira, Confluence
• Technical conception and further development of a modern Angular web application as part of the portal migration
• Built a modular frontend architecture with Nx and clear separation of domain and technical layers (Clean Architecture)
• Introduced and implemented Domain-Driven Design in the frontend context, including layer model and linting rules for code organization
• Developed reusable UI components and features using Angular, NgRx and RxJS
• Integrated the application with backend services via REST APIs
• Ensured high code quality through structured code reviews, testing with Jest and Cypress and introduction of guidelines
• Performed regular upgrades to new Angular versions to ensure long-term maintainability
• Collaborated closely with internal developers, product owners and stakeholders for requirements analysis and solution finding
• Supported the team through active knowledge transfer, review coaching and technical decision making
• Established a modular architecture with Nx & DDD as the technical foundation for future development
• Significantly improved test coverage through systematic introduction of Cypress and Jest tests
• Facilitated intensive collaboration with internal developers to build DDD structures and testing strategies
• Delivered a modernized UI focusing on clarity, usability and modern web technologies, achieving high acceptance by over 4,000 field staff
• Enabled parallel operation of the new Angular portal with the existing .NET system for phased migration of the sales process

• Development of Blazor-Server applications for data management
• Focus on unifying design and user experience
• Mentoring junior developers
• Establishing and consulting for coding guidelines and best practices
• Technologies: .NET 9, Blazor Server, MudBlazor, HTML, CSS, MS SQL Server (T-SQL, Views, Trigger, Stored Procedures, Table-Valued Functions), Entity Framework, Visual Studio, Scrum, agile, git

• Development of new simulator features and extension of existing modules using C++.

• GUI design and implementation with Qt for Windows, including redesigns to improve usability and workflow.

• Maintenance and expansion of existing codebase: refactoring, bug fixes, and modularization to support new capabilities.

• Version control using Git.

• Performance optimization of simulation to meet real-time constraints.

• Creating and maintaining documentation: technical comments, design docs, API references and user manuals.

• Led a redesign that improved operator workflow and reduced task completion time.

• Extended simulator architecture to support multiple new scenario types while preserving backward compatibility.

• Implemented refactoring and modularization that simplified maintenance and accelerated feature delivery.

• Technologies: C++03, Qt4.6, QMake, Git, V-Model, Windows

• Participated in the Riyadh Public Transport (KAPT) project introducing public transportation in Riyadh, supporting multimodal journeys combining bus, metro, car on demand.
• Worked via Thiqah and partnered with Andersen to refactor the mobile MaaS application DARB into a new microservices architecture under SCRUM framework, successfully completing Phase 1.
• Facilitated a team of 40 developers across Android, iOS, Web, Java, DevOps, architecture, analysis, and QA.
• Moderated Scrum events and communicated with the client, proactively reporting on project deadlines, scope, and challenges.
• Coordinated cross-team efforts between Thiqah specialists and GPS development teams, managing Jira and Azure DevOps trackers.
• Supported and improved Scrum processes throughout the project.
• Due to Thiqah’s takeover by Elm, subsequent phases were handled entirely in Saudi Arabia with GPS providing IT consulting.
• Tools: Azure DevOps, Jira, Confluence, Draw.IO, ChatGPT

• Design and implementation of a Laravel backend API for provider-based geo search, feature details, boundary geometries and neighborhood detection.
• The API serves as a server-side proxy, cache and enrichment layer, protecting credentials for external geo services and persisting features, localizations, geometries, hierarchies and neighborhood relationships in MariaDB.
• Key areas included normalization of autocomplete and feature data, caching strategies for expensive boundary/polygon requests, spatial processing of GeoJSON and MultiPolygon geometries, as well as neighborhood detection using hierarchies, bounding box filters and topology checks.
• Additionally, separate production and diagnostic endpoints were created, along with status and error catalogs, discovery logging, a Docker development stack, API documentation, and unit and feature tests.
• Technologies: PHP 8.3, Laravel, REST API, geo data API, GeoJSON, MariaDB Spatial, Eloquent, Laravel Queues, PHPUnit, Mockery, Docker, Docker Compose, API design, geocoding, boundary data, spatial queries.

I have worked across multiple international client projects, holding senior roles including Software Architect, Senior Software Developer, Technical Lead, and Lead Backend & DevOps Engineer. My experience spans complex enterprise environments in banking, financial services, telecommunications, engineering, and automotive domains, supporting organisations such as UniCredit Bank, Telefónica O2, and BMW.

At UniCredit Bank, within the Securities Domain Transformation program, I led the modernisation of legacy monolithic systems into cloud-native Spring Boot microservices and an Angular frontend deployed on Google Cloud Platform. Beyond implementation, I was responsible for defining the target architecture, producing system architecture diagrams and sequence diagrams, and preparing API contract documentation for clients. I designed RESTful APIs and integrated Apigee for secure and reusable cross-project service consumption of APIs. I architected Kubernetes-based deployments using Helm. CI/CD pipelines were built with Jenkins, automating code analysis using Sonar, as well as testing and deployment stages. Defining clean coding principles for the project, conducting regular code reviews, and mentoring junior developers were also among my tasks at UniCredit.

At Telefónica O2, I led the transformation of a legacy call centre desktop application into a cloud-native microservices and micro-frontend solution. I actively contributed to the platform architecture, creating system architecture diagrams, component diagrams, architecture documentation, and ADRs for future references. I improved the performance and scalability of the services. I optimised AWS infrastructure costs, particularly by minimising the use of DynamoDB and reusing test environments effectively. Observability was implemented using Prometheus, Grafana, CloudWatch, and Splunk dashboards. CI/CD pipelines were delivered using GitLab, Docker, Kubernetes, and AWS. Conducted techinical sessions for teams.

• Engage with stakeholders across departments to identify and document business needs, goals, and objectives.
• Conduct interviews, workshops, and surveys to gather comprehensive requirements for Salesforce solutions.
• Configure Salesforce products such as Sales Cloud, Service Cloud, Marketing Cloud, Health Cloud, and Data Cloud to align with the company's requirements.
• Analyze existing business processes and identify opportunities for improvement and automation within the Salesforce platform.
• Build campaigns, automation and journeys, data management, API and integrations, scripting and customization, analytics and reporting, introduction of generative AI capabilities.
• Develop custom applications using Apex, Visualforce, and Lightning Components; create and customize Salesforce objects, workflows, validation rules, and triggers; implement custom user interfaces using Lightning Web Components (LWC).
• Develop training materials and conduct training sessions to ensure effective user adoption of Salesforce solutions.
• Provide ongoing support to end-users, addressing issues and ensuring they are proficient in using Salesforce tools.
• Create and execute test plans, including unit testing, integration testing, and user acceptance testing (UAT).
• Identify and resolve issues, ensuring that Salesforce solutions meet business requirements and quality standards.
• Design and implement customized reports and dashboards to provide actionable insights and support data-driven decision-making and product delivery.