# Event-Driven Architecture > Use an event-driven, eventually consistent approach to maintain data consistency across services. - **Category**: Event Driven Architecture - **Subcategory**: core - **Canonical URL**: https://designpattern.fyi/patterns/event_driven_architecture/ --- ## Description **Context**: You have applied the Database per Service pattern. Each service has its own database. Some business transactions, however, span multiple services so you need a mechanism to ensure data consistency across services. For example, imagine you are building an e-commerce store where customers have a credit limit. The application must ensure that a new order will not exceed the customer's credit limit. Since Orders and Customers are in different databases owned by different services, the application cannot simply use a local ACID transaction. **Problem**: How to maintain data consistency across services? **Solution**: Use an event-driven, eventually consistent approach. Each service publishes an event whenever it updates its data. Other services subscribe to events. When an event is received, a service updates its data. This approach decouples services and enables asynchronous communication, improving scalability and resilience. ## Use Cases Use when you need to maintain data consistency across multiple services that each have their own database, and eventual consistency is acceptable. ## Trade-offs ### Advantages - Enables loosely coupled services that can be developed, deployed, and scaled independently - Improves availability since services don't need synchronous communication - Supports multiple subscribers for each event without modifying the producer - Naturally captures the history of state changes as a sequence of events ### Considerations & Drawbacks - Programming model is more complex than traditional ACID transactions - Eventual consistency may be confusing to users or require compensating logic - Events may be delivered out of order or duplicated, requiring idempotent consumers - Debugging and tracing distributed event flows is more difficult --- **Reference**: [Original Source](https://microservices.io/patterns/data/event-driven-architecture.html)