TENIOS GmbH

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

Cologne, Germany (hybrid)

Employee

Software development

€67,000 to €72,000 per year

We are looking for a Senior Java Engineer (m/f/d) to help design, build and operate the backend services behind our cloud communications platform — from architectural decisions to production operation.

They work in an interdisciplinary engineering organization and develop 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 and headquartered in Cologne, Germany. 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 all industries, in automating business processes with AI and cloud technology—for example, through AI-based voicebots.

Tasks

You will take on end-to-end responsibility (“you build it, you run it”) for our cloud-native communications platform — from call control to open-source telephony integrations and AI voicebots to the further development of the frontend.

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 voicebot connectivity: Integration of real-time AI voicebot platforms (WebSockets/RTP) into telephony workflows for automated conversation interactions and context-aware handoffs 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

Operation & 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 the European NIS-2 cybersecurity requirements.

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

Collaboration & further development

• Frontend maintenance & migration: Maintenance of existing management interfaces based on Backbone.js & Marionette.js, as well as management 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 delivery.

qualification

Must-have

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

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

• Experience in the design 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 foundations in quality practices: automated tests, 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

• Safe handling of production systems and incident response

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

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

Nice-to-have

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

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

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

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

Benefits