Field Notes From Payment Systems
Payment systems, ledgers, and compliance infrastructure have tight constraints. Transactions must be correct, auditable, and fast. Regulatory deadlines do not wait for rewrites.
This material draws on production experience scaling Klarna's payment infrastructure and later work with regulated startups across Europe. The recurring theme is simple: the system has to explain what happened, survive load, and leave a trail that auditors and engineers can read.
Useful topics tend to include:
- Ledger architecture review and append-only accounting design
- Performance analysis for high-throughput transaction processing
- Compliance infrastructure, audit trails, and cryptographic verification
- Migration planning from monolith to isolated, supervisable services
Resources
- Building Fintech Systems That Stay Fast and Stay Compliant (Code BEAM Berlin 2025 talk and presentation)
- Architecture and scale review when a live system needs outside reading
- Contact Erik about a fintech system
