System Overview - Order state machine
This system manages the lifecycle of an order in an e-commerce platform. It tracks the order status from creation to completion, ensuring valid state transitions and handling failures gracefully.
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Order state machine in LLD - Architecture Diagram
Architecture Diagram
User | v Order Service | v State Machine Engine | v Order Database | v Notification Service
Components
User
actor
Initiates order actions like create, cancel, or update
Order Service
service
Receives user requests and forwards them to the state machine
State Machine Engine
service
Manages order state transitions and validates state changes
Order Database
database
Stores order details and current state
Notification Service
service
Sends updates to users about order status changes
Request Flow - 5 Hops
User → Order Service
Order Service → State Machine Engine
State Machine Engine → Order Database
State Machine Engine → Notification Service
Notification Service → User
Failure Scenario
Component Fails:Order Database
Impact:Order state updates fail, new orders cannot be saved, but notifications and validations continue for existing cached states
Mitigation:Use database replication and fallback cache to serve read requests; queue write requests for retry when DB recovers
Architecture Quiz - 3 Questions
Test your understanding
Which component validates and manages order state transitions?
Design Principle
This design uses a dedicated state machine service to ensure all order state changes are valid and consistent. Separating state management from user request handling improves clarity and scalability. Notifications are decoupled to avoid blocking order processing.