About Marcus
I help companies build secure, self-hosted, and vendor-independent infrastructure using open-source technologies. My focus lies in end-to-end architecture, automation, and system hardening – from networking and virtualization to container orchestration and service delivery.
I work hands-on with technologies such as Linux (Debian, RHEL, Oracle Linux), KVM & Proxmox, Ceph block storage, WireGuard, OPNsense, OpenLDAP, and SELinux. For orchestration and deployment I use Kubernetes, Docker, Helm, Kustomize, GitOps, and Ansible – always with a clear focus on automation, reproducibility, and long-term maintainability.
In database-driven projects, I provide deep PostgreSQL expertise (HA, replication, monitoring, migration from Oracle), along with MariaDB, MySQL, and CI/CD integration. My clients trust me to plan, migrate, secure, and document infrastructures across critical systems.
In recent years, I’ve led major transitions such as:
– Replacing Microsoft Exchange/M365 with self-hosted mail platforms (Postfix, Dovecot, Rspamd, SOGo)
– Migrating from VMware to KVM under OLVM
– Deploying Kubernetes clusters for internal services with RBAC, secrets, volumes, and GitOps
– Converting legacy Oracle databases into XML/JSON-based data flows (Rheinmetall)
– Training and enabling internal teams to operate their own DevOps stacks
I’m passionate about clear documentation (Markdown, Bookstack), internal knowledge transfer, and building systems that don’t need me later.
Typical clients include public institutions, finance and insurance companies, and industrial organizations. I deliver results through structure, transparency, and a no-nonsense approach to operations.
German
Native or bilingual
English
Native or bilingual
Can work on-site
Dülmen (up to 50km), Bochum (up to 50km)
Experience
- Comelio GmbHIT Infrastructure Architect · Self-Hosting, Kubernetes & AutomationDIGITAL AND ITJanuary 2008 - Today (18 years and 6 months)Dülmen, GermanySince 2008, I have built and operated a fully self-hosted infrastructure platform for Comelio GmbH with high availability and independent service delivery. The environment includes virtualization with KVM and Ceph (multipath over fibre), Kubernetes for container orchestration, and automation via Ansible and Bash. Core services such as mail (Postfix, Dovecot, Rspamd, SOGo), documentation (Bookstack), groupware, and DevOps tools are fully self-managed. Security layers include SELinux, VPN (WireGuard), and firewalling with OPNsense. The setup includes browser-based training environments using Apache Guacamole and supports international use (Germany, Switzerland, India, US). Full technical documentation and internal knowledge bases are maintained in Markdown. This platform is both a testbed and production-grade system used in daily operations and for client-facing training.
- RheinmetallData Migration Specialist · Oracle to XML/JSON TransformationMECHANICAL ENGINEERINGJuly 2017 - December 2021 (4 years and 5 months)Düsseldorf, GermanyDelivered a multi-year data migration project at Rheinmetall, converting large and deeply nested Oracle datasets into structured XML and JSON formats. Designed complex target structures using XML Schema (XSD) and implemented multi-stage mappings using Altova MapForce. Automated transformation and validation workflows with Python scripts and job scheduling. Integrated schema validation, test data generation, and delta handling. Optimized performance for high-volume, repeatable migrations. Delivered clean, reusable mapping templates and ensured audit-proof documentation of all structures.
- UniventionLinux Administrator · Samba AD & Python AutomationDIGITAL AND ITDecember 2019 - July 2021 (1 year and 7 months)Bremen, GermanyDesigned and implemented a Samba-based Active Directory infrastructure using Univention Corporate Server (UCS). Integrated UCS into existing heterogeneous Linux and Windows environments. Developed Python-based automation tools for user and group provisioning, access rights, and backup workflows. Consulted on LDAP/Kerberos-based integration of third-party applications. Delivered structured technical documentation and provided handover sessions to internal administrators. Focused on secure, maintainable, and transparent identity and access management using open-source technologies.
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Education
- CKAD(Certified Kubernetes Application Developer)Ruhr Universität Bochum:StudiumCKAD(Certified Kubernetes Application Developer)
- CKA(Certified Kubernetes AdministratorCKA(Certified Kubernetes Administrator