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Order Rejection Analysis and Recommendations

Summary

The microservices are working correctly, but many orders are being rejected due to insufficient customer balance or insufficient stock. This document analyzes the root causes and provides recommendations.

Root Cause Analysis

1. Order Generation

Location: order-service/src/main/java/pl/piomin/order/service/OrderGeneratorService.java (line 29)

Orders are generated with:

  • customerId: Random between 1-100
  • productId: Random between 1-100
  • price: 100 × (1-5) = 100-500
  • productCount: 1-5 items

2. Payment Service Initialization

Location: payment-service/src/main/java/pl/piomin/payment/PaymentApp.java (line 47)

Customers are initialized with:

  • amountAvailable: Random between 100-1000
  • 100 customers total

Rejection Condition (line 27 in OrderManageService.java):

if (order.getPrice() < customer.getAmountAvailable()) {
    order.setStatus("ACCEPT");
}

3. Stock Service Initialization

Location: stock-service/src/main/java/pl/piomin/stock/StockApp.java (line 45)

Products are initialized with:

  • availableItems: Random between 10-1000
  • 1000 products total

Rejection Condition (line 28 in OrderManageService.java):

if (order.getProductCount() < product.getAvailableItems()) {
    order.setStatus("ACCEPT");
}

Why Orders Are Being Rejected

Payment Rejections

  • Orders range from 100-500 in price
  • Customers range from 100-1000 in balance
  • Probability: ~50% of orders will be rejected due to insufficient balance
    • Many customers with ~100-200 balance will reject orders with price 400-500

Stock Rejections

  • Orders request 1-5 items
  • Products have 10-1000 items available
  • Probability: Lower rejection rate (~5-15%)
    • Only happens when product stock is very low (10-20 items) AND multiple orders hit the same product

Combined Effect

When both services must approve (SAGA pattern):

  • Payment approval: ~50%
  • Stock approval: ~90%
  • Overall CONFIRMED rate: ~45% (0.5 × 0.9)

Recommendations to Increase Acceptance

Option 1: Increase Customer Balances (Recommended for Testing)

Modify payment-service/PaymentApp.java line 47:

Current:

int count = r.nextInt(100, 1000);  // 100-1000

Recommended:

int count = r.nextInt(1000, 10000);  // 1000-10000 (10x higher)

This will increase payment approval rate to ~95%+ and overall CONFIRMED orders to ~85%+.

Option 2: Increase Product Stock

Modify stock-service/StockApp.java line 45:

Current:

int count = r.nextInt(10, 1000);  // 10-1000

Recommended:

int count = r.nextInt(100, 10000);  // 100-10000 (higher baseline)

Option 3: Reduce Order Amounts

Modify order-service/OrderGeneratorService.java line 30:

Current:

o.setPrice(100 * x);  // 100-500

Recommended:

o.setPrice(50 * x);  // 50-250 (50% reduction)

Option 4: Combination Approach (Best)

  1. Increase customer balances: r.nextInt(2000, 10000)
  2. Keep stock at: r.nextInt(100, 1000)
  3. Reduce order prices: o.setPrice(75 * x) (75-375)

This will result in ~90%+ CONFIRMED orders.

How to Implement

  1. Restart the services (clear H2 databases):

    • Stop all running services
    • Delete the H2 database files (usually in /tmp/kafka-streams/ or similar)

  2. Apply one of the changes above

  3. Restart all services:

    • Zookeeper and Kafka
    • order-service, payment-service, stock-service

  4. Generate orders:

    POST http://localhost:8080/orders/generate

  5. Monitor logs for higher CONFIRMED rate

Current Behavior (Expected)

With current initialization:

  • CONFIRMED: ~45% ✅
  • REJECTED: ~50% (payment failures) ❌
  • ROLLBACK: ~5% (stock failures) ❌

Monitoring

Check order status in order-service:

GET http://localhost:8080/orders

Look for:

  • status='CONFIRMED' - Successful orders (good!)
  • status='REJECTED' - Both services rejected
  • status='ROLLBACK' - One service rejected (SAGA rollback)
  • status='ACCEPT' - Pending (waiting for join)

Logs to Watch

Payment Service (in terminal):

Found: Customer{id=X, amountAvailable=Y}

Stock Service (in terminal):

Found: Product{id=X, availableItems=Y}

Order Service (in terminal):

Output: Order{..., status='CONFIRMED'/'REJECTED'/'ROLLBACK'}

Conclusion

The system is working correctly! The rejection rate is due to the balance between:

  • Reasonable order amounts (100-500)
  • Conservative customer balances (100-1000)
  • Adequate but not excessive stock (10-1000)

For demonstration purposes, increase customer balances to see more CONFIRMED orders and verify the SAGA pattern is working correctly across all three services.