Senior Linux & VoIP Infrastructure Engineer - 100% Remote - 4h / day

Headquarters: Frankfurt, Germany
URL: https://www.lightupnet.de

Senior Linux & VoIP Infrastructure Engineer

Remote • Part-time (4h/day) • €1,000/month • Freelance

About Us

We are a European telecom company with roots as an ISP dating back to 1998. Since 2011, our business has been focused almost entirely on VoIP services, including call origination, termination, and global DID (virtual telephone numbers) services.

Our infrastructure is fully self-managed and built primarily on open-source software. We operate our own ASN, maintain BGP sessions with upstream providers, and run physical infrastructure in Germany and Switzerland.

Our small technical team is building new web-based telecom services, and we’re looking for a hands-on engineer to take full ownership of the infrastructure and move it forward.

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The Role

This is a hybrid Sysadmin / DevOps / VoIP operations role with full responsibility for our infrastructure.

You will be the primary technical owner of our systems, responsible for maintaining stability while gradually modernizing and improving the platform. This is a self-directed role suited for someone comfortable working independently and making practical technical decisions.

Your responsibilities will include:

• Full responsibility for Linux servers and virtual machines

• Planning and executing migration from legacy systems

• Operating and improving the VoIP stack (Asterisk, Kamailio)

• Providing infrastructure, tools, and environments for developers

• Testing new VoIP vendors and SIP connections

• Troubleshooting customer and routing issues

• Improving automation, monitoring, backups, and security

• Basic network operations (BGP environment, routers, switches)

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Current Environment

Infrastructure

• ~26 physical servers, ~40 VMs

• Additional VMs at external providers

• Locations: Frankfurt (primary), two sites in Switzerland

• Mix of CentOS 6/7 (majority), Ubuntu, and one legacy FreeBSD VM

Core Software

• MySQL, MariaDB, Galera Cluster

• Asterisk, Kamailio

• Apache, HAProxy, Varnish

• BackupPC

• tinydns, dnscache

• Nagios

• Joomla

Hardware & Network

• Supermicro servers (100%) with IPMI (KVM-over-IP)

• QNAP NAS systems

• Juniper M-series routers

• Juniper SRX routers

• HP 41xx switches

• Own ASN with BGP upstreams

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Requirements

Must have:

• Strong Linux system administration experience

• Ability to work independently and take ownership of systems

• Experience with virtualization and VM management

• Solid troubleshooting skills

• Perfect understanding of TCP/IP fundamentals

• Knowledge of SIP and RTP, or the ability to learn these protocols quickly

• Basic networking knowledge

• Excellent shell scripting (bash) and/or Python skills

• Ability to automate routine system administration tasks

• Fluent English (written and spoken) for daily team communication and video calls

Nice to have:

• VoIP/SIP experience (Asterisk, Kamailio, SBCs, etc.)

• DevOps or automation experience (Ansible, Docker, CI/CD)

• Experience modernizing legacy infrastructures

• Basic FreeBSD familiarity

• Additional programming experience (any language)

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Required Working Style & Tools

This is a hands-on, console-driven sysadmin role. Our environment is almost entirely command-line based, built on Linux and open-source telecom software.

You should be comfortable working in terminal sessions for most of your day, troubleshooting live systems, and editing configuration files directly.

If you do not use most of the following commands and tools on a regular basis, this role is probably not a good fit:

asterisk, awk, cat, cp, cut, df, diff, dig, grep, head, host, htop, ifconfig, iptables, kamctl, last, ls, mail, mailx, mkdir, mtr, mv, mysql, mysqldump, netstat, ping, pssh, pwd, rm, rsync, screen, sed, sngrep, sort, ssh, systemctl, tail, tcpdump, top, traceroute, vi, vim, vimdiff, w, who, whois, yum

This position is best suited fo