Christian Lehnert
Software Engineer & Security Specialist
Bern, Switzerland · Debian since age 12
Summary
I own systems end-to-end — from architecture and development to production hardening, security assessment,
and infrastructure automation. 6+ years shipping production backends in Java/Spring Boot, C#/.NET, and Python.
Active pentester training on TryHackMe and Hack The Box. I run enterprise-grade infrastructure as a homelab
since 2016: Dell VRTX blade cluster, Cisco switching, 8 VLANs, fully automated with Ansible. Currently building
MCP integrations connecting LLMs to security tools and external data sources. 75+ certifications.
Experience
Pentester & Software Developer
it-processing AG · Bern-Liebefeld
- Active penetration testing — vulnerability assessment, exploit research, bug bounty
- Software development since Jul 2024, promoted to pentester role Dec 2024
- Previously: Software Tester (aity AG project) — Feb–Sep 2025
Co-CEO & Co-Founder
AC Innovation Holding UG (Haftungsbeschränkt)
- Full technical responsibility at startup level — architecture through deployment
- Previously Senior Software Developer (Jan 2023 – Jun 2024)
CTO & Senior Software Developer
Vennie
- Led front-end and back-end projects, managed infrastructure, mentored team members
- API integration with OAuth, AWS services, performance optimization
- Roles: CTO (Jan–Jun 2024), Senior Dev (Oct 2023–Feb 2024), Backend Dev (Oct 2023–Jan 2024)
Full Stack Developer
phi...gmbh · Baienfurt
- Full-stack development with C#, ASP.NET Core, .NET MAUI
- Hands-on experience in both front-end and back-end technologies
Fachinformatiker für Anwendungsentwicklung
Stiftung Liebenau · Ravensburg
- Built AZN time tracking system: Spring Boot + Azure AD OIDC, role-based security, Memcached sessions
- Built room booking system: Spring Boot + Angular + Microsoft Graph API
- Led and transitioned multiple projects to fellow trainees
Freelance Software Developer
- Completed projects for individual clients while pursuing certifications
- Built Qt/C++ messaging app for Android — shipped and running in production
Debian User / Contributor
- User since 2012 (age 12), contributor since 2025. 14+ years of daily Linux usage.
Key Projects
homelab-orchestra
- Fully automated homelab with Ansible — Cisco switches, Debian servers, Raspberry Pis, VPS nodes
- Multi-vendor: cisco.ios collection for C2960S + ISR 1900. Vault-encrypted. Architecture Decision Records.
- Single make target deploys entire infrastructure: SSH keys, DNS, Docker, VPN, VLANs, CI/CD
fanix — ThinkPad Fan Controller
- Low-level C program reading sensors and CPU load, writing fan levels to /proc/acpi/ibm/fan
- Privilege-separated: root daemon + unprivileged CLI client over Unix domain socket
- Dual thermal curves (temperature + CPU load), 5-second hardware watchdog for crash safety
DBPipe — MSSQL to PostgreSQL Migration
- High-performance streaming pipeline using COPY FROM STDIN for throughput
- Auto-handles schema mismatches, column truncation, FK constraint ordering
- Docker + GitLab CI/CD + Testcontainers integration tests with real MSSQL/PostgreSQL
Homelab Infrastructure
- Dell VRTX with 3x M630 blades, Cisco C2960S, ISR 1900, WLC + Aironet APs
- VMware ESXi, 8 VLANs, 15+ Docker services, Hetzner offsite backups
- Zammad ticketing, Snikket XMPP, WikiJS, Uptime Kuma, Caddy TLS, WireGuard VPN
3
Servers
13
Endpoints
99.9%
Uptime
47
Repos
Technical Skills
Languages
Java, C#, Python, C/C++, Go, JavaScript, Dart
Backend
Spring Boot, ASP.NET Core, REST APIs, GraphQL, Node.js, Spring Security, Auth0/JWT
Infrastructure & DevOps
Ansible, Docker, Kubernetes, Jenkins, GitLab CI/CD, Caddy, VMware ESXi, Proxmox
Networking & Security
Cisco IOS, VLANs, WireGuard, Nmap, Wireshark, Burp Suite, OWASP, Pentesting
Cloud & Data
Azure, AWS, PostgreSQL, MongoDB, Oracle, SAP, Testcontainers
AI & Automation
MCP Servers, LLM Integration, Claude Skills, n8n, RAG, Prompt Engineering
Education
IHK Bodensee-Oberschwaben
Fachinformatiker für Anwendungsentwicklung
August 2021 – June 2024
Adolf Aich
Fachinformatiker für Anwendungsentwicklung, Information Technology
Languages
German (Native) ·
English (Professional Working) ·
Hebrew (Elementary) ·
Yiddish (Elementary)
Certifications (Selection of 75+)
.NET MAUI Essential Training ·
Software Architecture Foundations ·
AWS Monitoring, Logging & Remediation ·
Mastering SELinux ·
Securing Docker Containers ·
Kubernetes for Java Developers ·
Developing Secure Software ·
Threat Modeling ·
MCP: Hands-On with Agentic AI ·
RAG and Fine-Tuning ·
CRIMS Compliance Fundamentals ·
Linux: Storage Systems
Environment
Daily driver: Debian 12 + i3 WM ·
Editor: Vim ·
Shell: zsh ·
VCS: Git ·
IDE: IntelliJ IDEA ·
Pentest: TryHackMe · Hack The Box