Engineering Build Log

A running record of real backend engineering work — the problems, the constraints, the trade-offs, and what actually shipped. This is proof of work: the reasoning behind systems I build, written up as I go.

I'm David Abejirin, a backend engineer focused on payment systems, distributed systems, and reliability. Each entry below is a compact case study — a specific engineering decision, why it was hard, and how it was solved. Details are generalized to protect client and employer confidentiality; the engineering is real.

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Build Log · Architecture Jul 5, 2026

Architecting a multi-tenant fintech-as-a-service platform

A platform that onboards institutions to launch their own fintech. I built a custom annotation processor that auto-configures each tenant's domain and database, and chose a centralized data access proxy over a per-tenant routing library — cutting database connections and cost as tenants scale.

Multi-tenancy Annotation Processor Data Access Proxy Java Spring Boot Kafka

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Build Log · Payments Jul 5, 2026

A virtual account system with direct NIBSS integration

Dedicated virtual account numbers, direct integration with the interbank rails (no aggregator in the path), and real-time attribution and reconciliation — with an average transaction processing time of about 3 seconds.

Virtual Accounts NIBSS Payments Java Kafka

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Build Log · Core Banking Jul 5, 2026

Custom Apache Fineract core banking (CBA) setup

Setting up and configuring Apache Fineract as the ledgered system of record — chart of accounts, financial products, and GL mappings — so the platform runs on a proven, auditable core banking application instead of hand-built accounting.

Apache Fineract Core Banking General Ledger Java