Distributed payment processing platform

What needed solving

A payments business needed one platform to run initiation, authorization, capture, refunds, settlement and reconciliation across several payment providers. It could never double-charge a customer or lose an event.

How I approached it

• Designed the platform as independent microservices for initiation, authorization, transaction processing, refunds, settlement and reconciliation.
• Implemented the Saga pattern for distributed transactions, with compensating actions when a step fails.
• Implemented idempotent payment APIs, so client retries, network failures and redelivered messages never cause a duplicate charge.
• Used the Outbox pattern to keep database changes and published events in step.
• Built the event flows on EventBridge, SNS, SQS and Lambda, with retries, exponential backoff and dead-letter queues.
• Modelled the transaction lifecycle: initiated, authorized, captured, settled, failed and refunded.
• Put each provider's gateway API behind one internal contract, so adding a provider doesn't touch core services.
• Built reconciliation that flags mismatches between internal records and provider data, with automated recovery.
• Secured external APIs with API Gateway: validation, authentication, authorization, throttling and routing.
• Set up CI/CD, plus CloudWatch tracing, latency and payment metrics.
• Ran design reviews, set technical standards and guided the team on distributed-systems work.

Built with

• Node.js
• TypeScript
• Python
• FastAPI
• API Gateway
• Lambda
• EventBridge
• SNS
• SQS
• ECS Fargate
• CloudWatch
• IAM