Principal​/Staff Engineer, Systems & Billing Infrastructure

Company
keylight is a global subscription technology vendor founded in 2015, with offices in Berlin, Zurich, Belgrade, New York, and Singapore. The platform is the only user-centric, end-to-end solution on the market, streamlining recurring operations across commerce, sales, subscription management, billing automation, revenue and accounting automation, and advanced data analytics.

To support our growth, we are looking for a Principal Engineer who is passionate about building scalable systems and shaping the technical foundation of our global billing infrastructure. If you thrive on solving complex challenges at scale and want to make a real impact on a mission-critical platform, we’d love to hear from you.

Due to the nature of this role, candidates must reside in Berlin and hold legal authorization to work in Germany.

Principal/Staff Engineer Role overview

We are looking for an exceptional technical individual contributor to join our platform engineering team. This is a highly impactful role for someone who thrives on complex systems, deeply understands distributed architecture, and can architect scalable, resilient systems. You will play a key role in evolving our B2B SaaS subscription management and billing platform to handle high transaction volumes securely, reliably, and with low latency.

As Principal/Staff Engineer, you will own critical architectural decisions, guide system design, and mentor others through example. You'll collaborate across product, engineering, and infrastructure teams to design the foundation for the next stage of our platform’s scale. You are a pragmatic visionary who can translate business needs into workable technology solutions.

Principal/Staff Engineer Key responsibilities

• Design and evolve core platform architecture for scale, availability, and performance—especially across billing, invoicing, and event-driven processing pipelines.
• Develop scalable invoice generation and processing systems capable of handling multi-million daily volume.
• Architect high-throughput microservices, data pipelines, and distributed task scheduling systems.
• Write high-quality, maintainable code across core services (e.g., billing, pricing engine).
• Design and implement performant data models and event schemas for billing and subscription workflows.
• Collaborate with Dev Ops/SRE to define observability, alerting, and recovery strategies for mission-critical systems.
• Act as a technical owner for subsystems, guiding others through code reviews, design reviews, and architectural blueprints without having direct reports.

Must-Haves

• 8+ years of backend engineering experience, with at least 3 years in principal-level or similar roles.
• Proven experience designing and scaling distributed systems (e.g., Postgres SQL, Node.js, Typescript, Openapi, stream processing, eventual consistency).
• Deep understanding of financial systems, ledger integrity, and high-volume invoice or transaction processing.
• Architectural experience with high-throughput SaaS platforms, especially in the B2B and financial domains.
• Solid understanding of software architecture principles, design patterns, and best practices for building scalable and maintainable software.

Strong Plus

• Experience with multi-tenant SaaS architecture and usage-based billing models.
• Familiarity with idempotent systems, deduplication, and exactly-once semantics.
• Knowledge of GDPR, PCI-DSS, SOC2, and compliance in billing systems.
• Experience working on systems that scaled from thousands to millions of operations per day.

• An autonomous team player who enjoys working with others but is equally capable of independent thinking to drive progress.
• Proactive…