AtlasPay

Self-hosted payment infrastructure inspired by platforms such as Stripe and Paystack.

AtlasPay is a self-hosted payment infrastructure project designed with serious financial engineering principles. The system contains seven domains: Identity & Onboarding, Accounts, Ledger, Transfers, Cards, Limits, and Platform Access. The architecture enforces clear boundaries between Domain, Application, and Infrastructure layers, adhering to Hexagonal Architecture and Domain-Driven Design.

GitHub

Architecture — Hexagonal

Client  →  REST API  →  Application Service
                              ↓
                       Domain Layer
            (Identity · Accounts · Ledger · Transfers · Cards)
                              ↓
                Infrastructure Adapters
               PostgreSQL  ·  Kafka  ·  Redis

Tech Stack

Java 21Spring BootPostgreSQLKafkaRedisDockerGradle (Kotlin DSL)JUnitMockitoTestcontainersSpring Security

Key Features

Monetary correctness and financial transaction modeling
Double-entry accounting concepts in the Ledger domain
Transaction integrity, idempotency, auditability, and reconciliation
Event-driven payment flows using Kafka
Domain-Driven Design with bounded contexts and aggregates
Hexagonal Architecture (Ports and Adapters)
Strict concurrency control with pessimistic and optimistic locking

Engineering Challenges

Modeling money safely using Java BigDecimal.
Handling concurrency and transaction isolation to protect financial transactions.
Implementing reliable message handling and event-driven architecture.
Designing bounded contexts that enforce strict separation of concerns.

Key Learnings

Advanced Java backend engineering.
Deep practical application of Domain-Driven Design.
Financial engineering and monetary correctness.
Building resilient and observable distributed systems.