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Scheduler & Outbox Microservice

Purpose – Executes daily batch jobs (Spring Batch) and guarantees exact‑once publication of domain events using the Transactional Outbox pattern for the OrderHub platform.

This service processes scheduled orders every midnight (KST) and emits ORDER_SCHEDULED events without losing messages, even in the face of crashes or retries.

✨ Key Responsibilities

  1. Scheduled Order Collection – Persists snapshots of every order in scheduled_orders table (via Kafka listener).

  2. Nightly Processing – At 00:00 (cron 0 0 0 * * *) a Spring Batch job:

    • Reads yesterday’s PENDING scheduled orders (excluding cancelled).
    • Marks them as PROCESSING.
    • Writes an inventory-deduct event request to the Outbox table.

  3. Transactional Outbox – OutboxEvent rows are saved in the same DB transaction as batch writes, ensuring atomicity. A separate generic publisher (not shown) polls and pushes to Kafka.

🏗️ Tech Stack

Layer Technology
Runtime Java 17, Spring Boot 3
Batch Spring Batch (chunk‑oriented)
Persistence Spring Data JPA, MySQL 8
Messaging Apache Kafka (Outbox pattern)
Build Gradle 8, Docker Compose

⚙️ Batch Job Flow

graph TD
    subgraph Nightly Job (00:00)
        R[ItemReader: SELECT scheduled_orders<br/>where date=yesterday & status=PENDING]
        P[ItemProcessor:<br/>order.markAsProcessed()]
        W[ItemWriter:<br/>save orders + insert OutboxEvent]
    end
    R --> P --> W
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  • Reader – JPQL pulls yesterday’s orders using BETWEEN & ProcessStatus.PENDING filter.
  • Processor – Sets processStatus = PROCESSING (business marker).
  • Writer – Persists changes and builds an InventoryDeductRequest, wrapped as an OutboxEvent with eventType = ORDER_SCHEDULED.

Domain Model Snapshots

classDiagram
class OutboxEvent {
  +Long id
  +AggregateType aggregateType
  +String aggregateId
  +EventType eventType
  +String payload
  +EventStatus status
}

class ScheduledOrder {
  +Long id
  +Long originalOrderId
  +Long storeId
  +OrderStatus status
  +ProcessStatus processStatus
  +Instant scheduledAt
}
ScheduledOrder --> "*" ScheduledOrderItem
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Event Contracts

Topic Payload Trigger
order-created OrderEventRequest Order service
order-updated OrderEventRequest Order service
Outbox → inventory-deduct InventoryDeductRequest Scheduler batch job

Outbox publisher polls rows where status = PENDING, sends to Kafka, then sets status = PUBLISHED + publishedAt.

Running Locally

git clone https://github.com/orderhub/scheduler-service.git
cd scheduler-service

# start infra
docker compose up -d mysql kafka zookeeper

# run application (incl. @Scheduled cron)
./gradlew bootRun

Check logs around midnight or change cron to */30 * * * * * for quick tests.

Testing

  • Unit – JUnit 5 for domain & processor logic.
  • Integration – Testcontainers for MySQL+Kafka, verifying outbox insertion and message consumption.

Deployment

Built with Jib → pushed to registry → deployed via Helm chart. Cron schedule adjustable via SPRING_BATCH_CRON env.

© 2025 OrderHub