High-Availability Payment Gateway

A production-style backend payment gateway built using Spring Boot and PostgreSQL, designed with resiliency, transactional integrity, and CI/CD automation.

Tech Stack

• Java 21
• Spring Boot 3
• PostgreSQL
• JPA / Hibernate
• Resilience4j (Circuit Breaker)
• JUnit 5 & Mockito
• H2 (Test Isolation)
• GitHub Actions (CI/CD)
• Docker-ready

Key Engineering Features

• ACID-compliant transactional money transfer
• Idempotent transaction handling to prevent duplicate payments
• Optimistic locking for concurrent financial operations
• Circuit breaker pattern for external payment rail protection
• Full integration testing hitting real REST endpoints
• CI pipeline with automated test execution

Architecture Highlights

• Controller → Service → Repository layered design
• ExternalBankService protected by Resilience4j
• Separate test profile using in-memory H2 database
• Clean separation of production and test environments

Running Locally

1. Set environment variables: DB_USERNAME DB_PASSWORD

2. Run: ./mvnw spring-boot:run

Run Tests

./mvnw clean test

All tests execute automatically via GitHub Actions on push.

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Engineered for high-availability financial systems.