💳 MicroPay - Payment Service

MicroPay-Payment is the heart of MicroPay’s transaction flow ecosystem — a distributed, event-driven Wallet Application.

It manages and coordinates all payment-related transactions through Saga Orchestration and asynchronous communication between multiple microservices.

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🧩 System Context

MicroPay consists of six independent microservices:

Service	Description
Gateway	Central API gateway for routing and load balancing
Security	Handles authentication and authorization
Payment	Orchestrates the payment lifecycle
Wallet	Maintains wallet balance and reservations
Transaction	Records and tracks transaction states
Notification	Sends notifications to users

Four services — Payment, Wallet, Transaction, and Notification — communicate asynchronously via RabbitMQ.

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⚙️ Core Responsibilities

The Payment Service acts as the central coordinator for all transaction workflows.
It:

• Initiates, validates, and processes payment requests.
• Implements Saga orchestration to ensure distributed consistency.
• Coordinates asynchronous events across other microservices.
• Handles failure recovery and compensation logic.

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🔌 REST Endpoints

Endpoint	Method	Description
/transfer	POST	Wallet → Wallet transaction
/top-up	POST	External Provider → Wallet transaction
/withdraw	POST	Wallet → External Provider transaction

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🧠 Internal Design

To ensure scalability and extensibility, the Payment Service uses the Strategy Pattern for payment processing.

• Three core processor services:
  • TopUpProcessorService
  • TransferProcessorService
  • WithdrawalProcessorService

Two of them (TopUpProcessorService, WithdrawalProcessorService) use a strategy registry:

Map<PaymentKey, PaymentProcessor> registry;

This allows automatic processor selection based on payment source and destination type. New payment types can be added by simply registering a new processor — no changes to existing code.

🐇 Asynchronous Flow (Simplified)

• Payment Service initiates the transaction cycle.
• Coordinates processing and validation events.
• Updates wallet and transaction states asynchronously.
• Sends success/failure notifications at completion.

🚀 Deployment

All MicroPay services are:

• Built with Gradle
• Containerized using Docker
• Deployed and tested in Google Cloud Platform (GCP)
• Designed for Kubernetes orchestration

🧰 Tech Stack

• Java 21
• Spring Boot
• RabbitMQ
• PostgreSQL
• Redis
• Docker & Kubernetes
• Gradle
• JUnit & Mockito
• Prometheus & Grafana(later)

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Omar Ismailov
Software Engineer • Backend & System Design Enthusiast
Building reliable systems with simplicity and architecture in mind.