Banking Backend API
ACID-compliant banking engine that achieved zero balance drift under concurrent transaction testing.
The Problem
Race Conditions & Balance Drift
Traditional ledger systems fail under high concurrency due to race conditions and partial transaction failures. When multiple users transfer funds simultaneously, database read-write cycles can drift, leading to orphaned transactions and inaccurate ledger states. Building a financial backend requires ensuring absolute consistency, idempotency, and crash recovery, even during network disconnects or API failures.
The Solution
Immutable Ledger + 4-State Transaction Machine
Architected a double-entry bookkeeping ledger using MongoDB ACID transactions, 9 Mongoose pre-hook mutation guards, and a real-time state machine to process transactions through a strict workflow.
Key Technical Decisions
Impact & Results
Zero
Balance Errors
4 states
Transaction States
Zero Balance Drift Under Load
The financial backend achieved 100% data integrity with zero balance drift or database mismatch under simulated concurrent transfer tests. Audit logs recorded every ledger mutation, ensuring full accountability and compliance with double-entry accounting standards.
Key Learnings
Pre-hook mutation guards catch invalid database updates early — learned that validation at the API layer is not enough, database integrity must be protected at the model level.
Idempotency keys are non-negotiable for payment APIs — without unique client-side tokens, network retries lead to duplicate charges and ledger discrepancies.