Sr Software Engineer (Java) (m/f/d)

We are looking for a Senior Java Engineer (m/f/d) who will co-design, build, and operate the backend services behind our cloud communications platform – from architectural decisions to production operations.

You will work in an interdisciplinary engineering organization, developing distributed, cloud-native systems that support voice and messaging products for customers in the DACH region and internationally.

About Us

TENIOS GmbH is a licensed cloud communications provider founded in 2001, with its headquarters in Cologne. Since 2022, TENIOS has been part of the Apifonica Group, an Estonian provider of artificial intelligence (AI) and automation solutions. Our shared mission is to support companies worldwide across industries in automating business processes with AI and cloud technology – for example, through AI-based voice bots.

Responsibilities

You will take on end-to-end responsibility ("you build it, you run it") for our cloud-native communications platform – from call control and open-source telephony integrations to AI voice bots and frontend development.

Concept & Development

• Call Control & Telephony Engines: Development and maintenance of low-latency call control systems that work directly with open-source softswitches and SIP proxies (FreeSWITCH, Kamailio) – including advanced ACD (Automatic Call Distribution) engines and AI-powered IVR workflows

• AI Voice Bot Integration: Integration of real-time AI voice bot platforms (WebSockets/RTP) into telephony workflows for automated conversation interactions and context-aware handovers to human agents

• Backend & Multi-Tenancy Platform Development: Further development and scaling of our existing backend platform with modern Java-21+/Spring-based microservices and event-driven messaging (RabbitMQ) – continuous expansion of multi-tenant capabilities (isolation, metering, resource partitioning) as well as maintenance and further development of automated usage rating, billing, and invoicing engines

Operations & Reliability

• Secure Coding & Compliance: Application of strict secure coding practices (OWASP, Threat Modeling, Dependency Scanning) to ensure the platform's compliance with the ISO 27001 certification standard and European NIS-2 cybersecurity requirements

• DevOps & Cloud Resilience: Management of automated CI/CD pipelines, Kubernetes deployments, and observability to ensure availability of 99.99%+

**
Collaboration & Further Development**

• Frontend Maintenance & Migration: Maintenance of existing management interfaces based on Backbone.js & Marionette.js, and leadership of the planned migration to modern frontend frameworks

• AI-powered Development: Active use and promotion of modern AI development tools and agent-based CLI workflows (e.g., Claude Code) to accelerate coding, refactoring, and software deployment

Qualifications

Must-have

• At least 5 years of professional experience in software development with a strong focus on Java-based backend systems

• In-depth knowledge of modern Java (17/21+), Spring Boot, Spring Framework, JPA/Hibernate, and RESTful API design

• Experience in the conception and implementation of distributed, cloud-native applications with microservices

• Practical experience with Docker, Kubernetes, and at least one modern CI/CD tool (e.g., GitHub Actions, GitLab CI, Jenkins, Argo CD)

• Experience with at least one major cloud platform (AWS, Azure, or GCP)

• Solid foundation in quality practices: automated testing, code reviews, CI/CD

• Good understanding of secure development practices (OWASP Top 10, Dependency & Secrets Management)

• Experience with observability tools: metrics, centralized logging, distributed tracing, APM

• Proficient in operating production systems and responding to incidents

• Strong analytical thinking and sound technical decision-making in complex distributed systems

• Fluent English skills (written and spoken); German language skills are an advantage

Nice-to-have

• Practical experience with AI-powered development tools (e.g., Claude Code, GitHub Copilot) – or a genuine openness to use them

• Experience with CPaaS or cloud communications platforms, telecommunication protocols (SIP, RTP, WebRTC), or related open-source frameworks (FreeSWITCH, Kamailio, Asterisk)

• Knowledge in the area of carrier-grade, highly available, low-latency distributed systems

• Experience with asynchronous messaging / event-driven architectures (Kafka, RabbitMQ)

Benefits

What we offer

• Gross annual salary of 67,000 to 72,000 Euros, depending on experience

• Hybrid work model with location in Cologne

• An international B2B technology environment: collaboration with customers from various European markets in a fast-growing technology company

• Focus on artificial intelligence and technology: daily work with state-of-the-art AI solutions and digital tools

• An influential team: an international, highly productive team with fast decision-making processes and a tangible impact on the company's growth

Good to know

• You will take on end-to-end responsibility – from concept to production operations

• Cloud-native and DevOps knowledge (Kubernetes, CI/CD, Observability) is as important as solid Java skills

• You will work closely with Platform Engineering, Security, and Product – a collaborative, not isolated role

• Our core business is telecommunications and cloud communications – a telecom background is a big plus, but not a prerequisite

• We use AI-powered development tools as an integral part of our daily work and expect openness towards them

Note: Passages in parentheses are placeholders and should be filled with concrete information (salary, contract type, application process) before publication.

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