Design patterns in microservices

 Here are the most important and commonly used design patterns in microservices

1. Saga Pattern

Purpose: Handle distributed transactions across multiple microservices
Type: Choreography or Orchestration
Use Case: Order → Payment → Inventory → Shipping with rollback on failure

2. Circuit Breaker Pattern

Purpose: Prevent system overload and failures from cascading

How: If one service is down, stop calling it temporarily (open the circuit)

Library: Resilience4j, Hystrix (legacy)

Use Case: Call to Payment Service fails 3 times → short-circuit and fallback

3. Retry Pattern

Purpose: Automatically retry failed calls a few times before failing

When to use: Temporary network glitch, slow downstream service

Tool: Resilience4j retry module

4. Bulkhead Pattern

Purpose: Isolate failures by partitioning the system (like compartments in a ship)

Use Case: One slow service should not block others

How: Allocate different thread pools/queues to services

5. API Gateway Pattern

Purpose: Single entry point for all external requests

Responsibilities: Routing, Auth, Rate limiting, Logging

Tool: Spring Cloud Gateway, Kong, Zuul, AWS API Gateway

6. Service Discovery Pattern

Purpose: Automatically find and route to services without hardcoding IPs

Tools: Eureka, Consul, Kubernetes DNS

7. Strangler Pattern

Purpose: Gradually migrate a monolith to microservices

How: Route certain functionalities to new services while keeping old monolith running

Tool: API Gateway with routing rules

8. Sidecar Pattern

Purpose: Deploy helper tools (e.g., logging, proxy, security) alongside app container

Use Case: Istio (Envoy sidecar), Fluentd logging agent

9. Aggregator Pattern

Purpose: One service calls multiple microservices, aggregates their responses

Use Case: UI needs data from User, Product, Order services → one gateway combines it

10. Command Query Responsibility Segregation (CQRS)

Purpose: Separate write (command) and read (query) models for scalability and speed

Use Case: Event sourcing + read replicas

11. Event Sourcing Pattern

Purpose: Store changes as a sequence of events, not just current state

Use Case: Banking apps, audit trails

Tool: Axon, EventStore

Summary Table

Pattern	Purpose
Saga	Handle distributed transactions
Circuit Breaker	Prevent cascading failures
Retry	Temporary recovery
Bulkhead	Failure isolation
API Gateway	Entry point for clients
Service Discovery	Dynamic service location
Strangler	Migrate monolith to microservices
Sidecar	Attach helper components
Aggregator	Combine responses from services
CQRS	Separate read/write models
Event Sourcing	Store history as events