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Microservicessystem_design~12 mins

CQRS pattern in Microservices - Architecture Diagram

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System Overview - CQRS pattern

The CQRS (Command Query Responsibility Segregation) pattern separates the system into two parts: one for handling commands (writes) and another for handling queries (reads). This helps improve scalability and performance by optimizing each side independently.

Key requirements include handling user requests to update data and fetch data efficiently, while keeping the system consistent and responsive.

Architecture Diagram
User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +---------------------+
  |                     |
Command Service     Query Service
  |                     |
  v                     v
Command Database     Query Database (Read-Optimized)
  |
  v
Message Queue
  |
  v
Event Handler
  |
  v
Query Database (Read-Optimized)
Components
User
actor
Initiates commands and queries
Load Balancer
load_balancer
Distributes incoming requests evenly to API Gateway instances
API Gateway
api_gateway
Routes commands and queries to appropriate services
Command Service
service
Handles write operations and updates data
Query Service
service
Handles read operations and returns data
Command Database
database
Stores the authoritative data for writes
Message Queue
message_queue
Asynchronously sends events from Command Service to update Query Database
Event Handler
service
Processes events from the queue to update the Query Database
Query Database (Read-Optimized)
database
Stores data optimized for fast read queries
Request Flow - 12 Hops
User → Load Balancer
Load Balancer → API Gateway
API Gateway → Command Service
Command Service → Command Database
Command Service → Message Queue
Message Queue → Event Handler
Event Handler → Query Database (Read-Optimized)
API Gateway → Query Service
Query Service → Query Database (Read-Optimized)
Query Service → API Gateway
API Gateway → Load Balancer
Load Balancer → User
Failure Scenario
Component Fails:Message Queue
Impact:Events about data changes are not delivered to update the Query Database, causing read data to become stale.
Mitigation:Implement message queue replication and retry mechanisms; use monitoring and alerts to detect failures and fallback to direct sync if needed.
Architecture Quiz - 3 Questions
Test your understanding
Which component handles write operations in the CQRS pattern?
AAPI Gateway
BCommand Service
CQuery Service
DEvent Handler
Design Principle
The CQRS pattern separates read and write workloads to optimize performance and scalability. Writes update the authoritative data and asynchronously propagate changes to a read-optimized database, enabling fast queries without impacting write performance.