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Linux System Administrator (f/m/d) Defense Products

IONOS SE
Network Administration
Berlin
Full-time
I-1567

About IONOS SE

At IONOS, we don't just manage servers – we shape the digital future for more than 6.2 million customers worldwide with our solutions. As Europe's leading hosting provider and a pioneer in independent cloud solutions, we are building next-generation infrastructure – from sovereign cloud architectures and high-performance GPU clusters to integrated AI automation tools. What drives us is digital sovereignty for Europe and real impact for small and medium-sized businesses (SMBs) as well as large enterprises. We work in agile teams, rely on transparent structures, and believe that excellence and innovation only emerge through true team spirit. Ready for your next step? Become part of IONOS and grow with us.

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United Internet Office Building

Tasks

Join our highly motivated team of experts dedicated to combating cybersecurity threats. As a System Administrator, you will plan and operate our cutting-edge defense platforms alongside site reliability engineers and network engineers. These platforms are crucial for protecting our hosting products and infrastructure, encompassing classic DDoS mitigation, modern Web Application Firewalls (WAF), Zero Trust strategies, and our Content Delivery Network (CDN). We foster a culture that highly values creative ideas, agile working methods, initiative, and participation.

As an Specialist in our Defense squad, you act as a vital shield against daily DDoS and sophisticated cyber attacks. You are the first line of defense, dedicated to neutralizing threats through technical mastery and proactive mitigation.

We are hiring for this role in Karlsruhe and/or Berlin. You will join a distributed, international Defense Platform Services team of approximately 8–9 experts. You will work within specialized squads for Operations, SRE, and NRE to provide comprehensive protection for the group’s infrastructure across Germany and beyond.

The day-to-day operations of the Defense Platform Services team directly correlate to the financial stability of the United Internet Group. When our defenders succeed, the group’s digital economy remains fluid; your success is measured by the silence of a neutralized threat.

  • Active Defense & DDoS Mitigation: Administer and troubleshoot scrubbing platforms and a complex, large-scale proxy infrastructure. You will engage in the "cat and mouse game" of fighting attacks in real-time—identifying, washing, and neutralizing malicious traffic to protect core cloud and fiber services.
  • Architectural Density & Operational Excellence: You will manage the lifecycle of 800+ Linux-based components within a highly available infrastructure. To maintain 24/7 group-wide protection, this role requires a mandatory on-call service rotation of one week per month, ensuring immediate response to high-priority network threats.
  • Innovation & Data-Driven Defense: We leverage modern AI tools for log analysis and pattern detection. You will bring creative ideas to the table, utilizing the ELK Stack and ClickHouse to manage high-volume telemetry, identify attack signatures, and devise advanced mitigation strategies.
  • Lifecycle & Pipeline Management: Develop and optimize CI/CD pipelines in an agile DevOps environment. You will evaluate and integrate new technologies—including Docker and Kubernetes—to ensure our defense architecture remains lean, efficient, and ahead of evolving industry threats.

Qualifications

Because this role manages critical national and corporate infrastructure, the barrier to entry involves both technical mastery and a high degree of professional trust.Therefore, we require 3 to 5 years of platform operating experience at scale. We are looking for an administrator with a "security gene"—a specialized, proactive interest in DDoS mitigation and cyber defense that goes beyond standard system maintenance.

  • Expert-level proficiency in managing complex, distributed Linux environments.
  • Proven experience configuring Nginx as a reverse proxy or Web Application Firewall (WAF).
  • Practical knowledge of BGP, Flowspec, and Anycast routing.
  • A passion for eliminating repetitive tasks through Ansible, Puppet, and Python.
  • Several years of experience in the administration of complex, distributed Linux systems.
  • Proven experience in configuring and operating Nginx as a reverse proxy or web application firewall.
  • Hands-on experience with the deployment of BGP, Flowspec, and Anycast routing on Linux systems and network routers.
  • Strong passion for automation using tools like Ansible, Puppet, and Python to eliminate repetitive manual tasks.
  • Strong analytical skills to evaluate DDoS attacks, implement effective countermeasures, and continuously develop our defense platforms.
  • Initial experience with technologies such as Docker, Kubernetes, ClickHouse, or the ELK Stack is beneficial.
  • Like us, you are a strong advocate for Open Source, especially Linux.

Benefits that make a difference

As an employer, United Internet offers interesting roles with exciting projects, personalized development opportunities and excellent career prospects.

Culture

Our working environment is characterized by flat hierarchies and short decision-making processes. We encourage a positive approach to learning from mistakes and open feedback!

Mobility

To support sustainable and flexible mobility, we provide our employees with attractive benefits packages. For example, through JobRad, you can lease your ideal bike on attractive terms. We also provide a financial subsidy for this offer. Alternatively, you can use public transport and benefit from a subsidy towards the Deutschlandticket.

Events

We celebrate our successes as a team: at United Internet, we throw legendary parties. And our varied workshops and team events foster a special sense of camaraderie.

Flexible Working

Many of our roles allow for remote working from home and flexible working hours.

Pension and health

Our employees benefit from attractive pension schemes. These include modern financial security options that support wealth accumulation. Our health and fitness programmes, covering topics such as ergonomics, exercise and nutrition, round off the package. The aim is to provide a working environment in which all colleagues can not only develop professionally but are also well-positioned for their personal future. 

Discounts

Our employees benefit from a wide range of discounts on our Group’s products and services, for example in the form of discounted broadband and mobile phone contracts. In addition, we offer exclusive price advantages for selected leisure and partner offers.

A wide range of training opportunities

Strengths are individual – and that is a good thing! Our wide range of development programmes offers excellent opportunities for personal and professional growth. From e-learnings to trainings, conferences and mentoring – we learn from, for and with one another to grow together.

Technology

To provide our employees with a productive and comfortable working environment, we rely on state-of-the-art technology. This includes high-performance hardware, ergonomic accessories and the latest software tools for efficient collaboration.

Our benefits in detail

  • Hybrid working model.
  • Flexible working hours through trust-based working hours.
  • Subsidized canteen and various free drinks at select locations.
  • Modern office space with excellent public transport connections.
  • Various employee discounts for activities and products.
  • Employee events such as summer and winter parties, as well as workshops.
  • Numerous training and development opportunities.
  • Various health offerings, such as sports and wellness courses.

Join our team

United Internet offers diverse opportunities for people who want to help shape the digital future. Those who want to contribute their strengths and grow in an innovative environment will find the right place with us.

apply online now

Two colleagues in the office
WORK UNITED.
 

Diversity enriches. Different cultures, nationalities, genders, ages, sexual orientations and religions as well as people with disabilities - we value diversity and encourage it. Because only teams that reflect all facets of society offer the best environment for creativity and make a company productive and distinctive. We value diversity and welcome all applications.

Contact

Questions?

IONOS SE
Recruiting Team IONOS

Hinterm Hauptbahnhof 3-5
D-76137 Karlsruhe
jobs@ionos.com

Please submit your application exclusively through our easy-to-use online application form. This allows us to ensure a transparent application process while maintaining full compliance with all applicable data protection regulations. Unfortunately, we are unable to accept applications submitted via email for the reasons outlined above.