Distributed Payment System Architecture & Ledger Design
System Flow Diagram
Client Checkout → Payment API → Message Queue (Kafka) → Processor Worker
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Payment Gateway API
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Double-Entry LedgerRequest Workflow & Logic
The client initiates a checkout. The Payment API saves a pending transaction and pushes a job to Kafka. The Processor Worker picks up the job, connects to the payment gateway (Stripe), collects the funds, and writes debit/credit entries to the database inside a database transaction block.
Engineering Considerations
Event Idempotency
Every transaction request uses a unique token to prevent double-billing customer cards.
Ledger Immutability
No UPDATE statements are allowed in ledger tables. Account balance changes are written as new transactions.
Reconciliation Loops
Nightly cron jobs compare local ledger logs with gateway transaction records to flag discrepancies.
Recommended Infrastructure Stack
| Service | Purpose / Role |
|---|---|
| PostgreSQL RDS | Stores double-entry transaction ledgers with ACID guarantees. |
| Apache Kafka | Handles transaction queues with strict ordering guarantees. |
| AWS Lambda | Executes lightweight transaction reconciliation cron jobs. |
Security Isolation Policy
Encrypt bank fields using AES-256 and restrict access to ledger databases via isolated subnets.
DevOps & Deployment Configuration
Monitor transactions with Datadog alert systems that flag elevated payment failure rates.