Lead Senior Backend Engineer (m/f/d)

Telekom; La Coruña; Hybrid; EUR 90,000 - 110,000; Full time

Benefits offered by this job

Hybrid work model (remote/on-site)

Flexible working hours

26+ vacation days

Job summary

T-Systems Iberia is seeking a Lead Senior Backend Engineer to design and maintain scalable backend platform services behind AI inference endpoints. You will architect multi-tenant systems for authentication, API key management, usage metering, billing, and request proxy.

Responsibilities include building core services with Python (FastAPI), implementing telemetry, security, and CI/CD pipelines, and collaborating with ML infrastructure teams to ensure secure, observable, and high-performance

Qualifications

• Senior backend experience in production scale environments
• Strong knowledge of Python async programming and tooling
• Experience with REST, gRPC, WebSockets, and SSE protocols
• Design authentication and authorization systems and API key management
• Experience with cloud providers and container orchestration (Docker, Kubernetes)
• Active collaboration in international teams

Responsibilities

• Design and build core platform services: API gateway, authentication, key rotation, multi-tenant isolation
• Develop APIs and backends using Python (FastAPI preferred)
• Implement usage metering, billing integration, and rate limiting
• Build scalable microservices for data processing and AI integration
• Operate high-throughput proxy/routing for model serving traffic
• Institute telemetry and observability with logs, traces, metrics, alerts
• Set high engineering standards: tests, CI/CD, deployment
• Collaborate with ML infra to integrate with model serving systems

Skills

Python

FastAPI

REST APIs

Distributed systems

Cloud infrastructure

Docker

Kubernetes

OAuth2/JWT/API keys

AWS/GCP/Azure

SQL/ORM

English communication

Education

Computer Science/Software Engineering degree

Tools

Git

Prometheus/Grafana/OpenTelemetry

Redis

nVidia Dynamo/vLLM/TensorRT-LLM integrations

Job description

Job ID: 744000153443026Lead Senior Backend Engineer (m/f/d)A Coruña, Bilbao, Gijón, Granada, Madrid, Reus, Seville, ValenciaProfessionalRegularT-Systems IberiaYour TaskWe are looking for a senior backend engineer with strong system design skills and experience building production infrastructure. This role involves architecting and maintaining backend platform services behind AI inference endpoints - a multi-tenant system handling authentication, API key management, usage metering, billing and request proxy. This is a high-ownership role where you will shape architecture decisions, raise the bar of engineering quality and build systems that are performant, secure and observable at scale. You'll collaborate with experts in AI infrastructure and data engineering to build robust, secure, and efficient systems that scale to millions of requests.ResponsibilitiesDesign and build core platform services: API gateway, authentication, authorization, key rotation, and multi-tenant isolationDesign, implement, and optimize APIs and backend systems using Python frameworks such as primarily FastAPI (or Flask, or Django)Architect and implement usage metering, billing integration, and rate limiting for inference endpointsBuild and maintain scalable, fault-tolerant microservices for data processing and AI integrationBuild and operate a high-throughput proxy/routing layer for AI model serving trafficCollaborate with cross-functional teams to design system architecture and ensure seamless system interoperabilityDesign telemetry and observability into the platform from the ground up — structured logging, distributed tracing, metrics, and alertingImplement robust CI/CD pipelines, monitoring, and observability for high-performance production systemsDrive technical decisions on architecture, data modeling, and technology choicesIdentify performance bottlenecks and drive improvements in reliability, scalability, and latencyEstablish engineering standards for the backend codebase: testing, code review, CI/CD, and deployment practicesEnsure best practices for security, compliance, and maintainability across the API lifecycleCollaborate closely with the ML infrastructure team to integrate with model serving systems (e.g., NVIDIA Dynamo, vLLM, SGlang, TensorRT-LLM)Your ProfileWe are seeking a Senior Backend Engineer / Python Developer with extensive experience in building and operating production backend systems at scale, strong system design skills, and deep expertise in distributed systems and API development. The ideal candidate will have proven experience with authentication systems, cloud infrastructure, and modern Python development.Must Have SkillsDegree in Computer Science, Software Engineering, or equivalent professional experience5+ years of experience building and operating backend systems in production with meaningful scale5+ years of experience developing backend systems with a focus on API design and high-scale production environmentsStrong proficiency in Python with deep knowledge of asynchronous programming, modern Python tooling and profilingProficiency in at least one systems-oriented language (Go, Rust, Java, C++)Willingness to work across the current stack which includes Python (FastAPI)Proven experience designing and maintaining REST APIs in production environmentsExperience with REST, gRPC, WebSockets, and SSE protocols and understanding of the tradeoffs between themExperience with websockets, SSE, and WebhooksSolid understanding of distributed systems including consistency, fault tolerance, concurrency, performance and networkingSolid understanding of data pipelines and performance optimizationExperience designing authentication and authorization systems (OAuth2, JWT, API key management, RBAC/ABAC)Experience with cloud infrastructure (AWS, GCP, or Azure)Experience with containerized environments (Docker)Experience with container orchestration (Kubernetes)Understanding of database design (SQL, ORMs etc.) and data modeling at scaleFluent in English (written and verbal)Comfortable collaborating in international teamsNice to Have SkillsExperience with high-throughput, low-latency or real-time systems (e.g., message queues, event-driven architectures)Familiarity with generative AI or large language models (e.g., integration of AI APIs, RAG workflows, or vector databases)Knowledge of modern DevOps practicesExperience with infrastructure as codeKnowledge of GitOps workflowsExperience with observability tools (Prometheus, Grafana, OpenTelemetry)Exposure to ML serving infrastructure (model servers, GPU scheduling, inference optimization)Comfortable occasionally touching or contributing to frontend code when necessaryExperience in stress/load-testing and evaluating performance of production systemsStrong problem-solving mindset and commitment to code quality and performance excellenceTrack record of improving engineering culture: mentoring junior engineers, introducing better practices, leading technical discussionsAbout UsT-Systems is part of the Deutsche Telekom Group, with around 30,000 employees worldwide. We create technology with purpose to generate a positive impact on society. We are looking for curious talent, eager to learn, take on challenges, and contribute ideas that transform our customers' experience.We trust people: we offer autonomy, continuous support, and a collaborative environment where you can grow without limits. We are one global team, guided by respect, integrity, and a passion for doing better every day.BenefitsWork environment & flexibilityInternational, dynamic and collaborative environmentT-Social: social initiatives (sports, community, health)Hybrid work model (remote/on-site)Flexible working hoursGrowth & developmentCustomized training: access to Coursera to learn whatever you want, whenever you wantWeekly language classes (English, Spanish & German)International Mentoring Sessions & Experience DaysCompensation & benefitsFlexible compensation plan (health insurance, meal vouchers, childcare, transport)TelemedicineLife and accident insuranceSocial fundWellbeing & time off26+ working days of vacation per yearFree access to specialist services (medical, legal, wellness)100% salary coverage during medical leaveApplication InformationIf you are looking for a new challenge, do not hesitate to send us your CV! Please send CV in English.Additional DetailsT-Systems Iberia will only process the CVs of candidates who meet the requirements specified for each offer.Job BenefitsOffice PerksFlexible compensation plan (meal vouchers, childcare, transport)T-Social: social initiatives (sports, community, health, ...)Professional DevelopmentCustomized training: access to Coursera to learn whatever you want, whenever you wantWeekly language classes (English, Spanish & German)International Mentoring Sessions & Experience DaysWork-Life BalanceHybrid work model (remote/on-site)Flexible working hours26+ working days of vacation per yearLifestyle & WellnessFree access to specialist services (medical, legal, wellness)Social fundHealth & InsuranceFlexible compensation plan (health insurance)Life and accident insuranceTelemedicine100% salary coverage during medical leave