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Microservicessystem_design~12 mins

Eventual consistency handling in Microservices - Architecture Diagram

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System Overview - Eventual consistency handling

This system manages data updates across multiple microservices that do not update their data stores instantly. It ensures that all services eventually have consistent data by using asynchronous communication and retries.

Key requirements include handling temporary data mismatches gracefully and ensuring data synchronization without blocking user requests.

Architecture Diagram
User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
+----------------+       +----------------+       +----------------+
|  Service A     |<----->|  Message Queue |<----->|  Service B     |
| (Command)      |       | (Event Broker) |       | (Query)        |
+----------------+       +----------------+       +----------------+
       |                                              |
       v                                              v
+----------------+                             +----------------+
| Database A     |                             | Database B     |
+----------------+                             +----------------+
Components
User
user
Initiates requests to the system
Load Balancer
load_balancer
Distributes incoming requests evenly to API Gateway instances
API Gateway
api_gateway
Routes requests to appropriate microservices
Service A
service
Handles commands and writes data to Database A
Message Queue
message_queue
Asynchronously transfers events from Service A to Service B
Service B
service
Consumes events and updates Database B to reflect changes
Database A
database
Stores authoritative data for Service A
Database B
database
Stores data for Service B, eventually consistent with Database A
Request Flow - 8 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Service A
Service A → Database A
Service A → Message Queue
Message Queue → Service B
Service B → Database B
Service B → API Gateway
Failure Scenario
Component Fails:Message Queue
Impact:Events are delayed or lost, causing Service B's data to be stale and inconsistent with Service A
Mitigation:Use durable queues with retry and dead-letter mechanisms to ensure eventual delivery; monitor queue health and alert on failures
Architecture Quiz - 3 Questions
Test your understanding
Which component ensures that Service B eventually receives updates from Service A?
ALoad Balancer
BAPI Gateway
CMessage Queue
DDatabase A
Design Principle
This architecture demonstrates the principle of eventual consistency by decoupling services with asynchronous messaging. It allows services to operate independently and update their data stores at different times while ensuring data synchronization over time.