Identifying service boundaries in Microservices - Architecture Diagram

System Overview - Identifying service boundaries

This system demonstrates how to divide a large application into smaller, independent microservices by identifying clear service boundaries. Each service handles a specific business capability, enabling easier development, deployment, and scaling.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +----------------+----------------+----------------+
  |                |                |
  v                v                v
Order Service   Inventory Service  Payment Service
  |                |                |
  v                v                v
Order DB       Inventory DB      Payment DB
  |
  v
Cache (Redis)

Components

User

client

End user interacting with the system

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to appropriate microservices based on URL and handles authentication

Order Service

service

Manages order creation, updates, and retrieval

Inventory Service

service

Manages product stock levels and availability

Payment Service

service

Handles payment processing and transaction status

Order DB

database

Stores order data for Order Service

Inventory DB

database

Stores inventory data for Inventory Service

Payment DB

database

Stores payment transaction data for Payment Service

Cache (Redis)

cache

Speeds up frequent reads for order data

Request Flow - 15 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Order Service

Order Service → Cache (Redis)

Cache (Redis) → Order Service

Order Service → Order DB

Order Service → Inventory Service

Inventory Service → Inventory DB

Order Service → Payment Service

Payment Service → Payment DB

Payment Service → Order Service

Order Service → Cache (Redis)

Order Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Inventory Service

Impact:Stock updates fail, orders may be accepted without reducing inventory, causing overselling

Mitigation:Implement circuit breaker in Order Service to detect Inventory Service failure and reject orders or queue them for later processing

Architecture Quiz - 3 Questions

Which component routes user requests to the correct microservice?

A Cache

B API Gateway

C Load Balancer

D Database

Design Principle

This architecture shows how to split a system into microservices by defining clear boundaries around business capabilities. Each service owns its own data and communicates asynchronously or synchronously with others, improving scalability and maintainability.

Practice

1. Which of the following best describes the primary goal when identifying service boundaries in microservices?

easy

A. Create services based on the number of developers available

B. Split services evenly by code size

C. Group all database operations into one service

D. Divide the system based on business capabilities and data ownership

Solution

1. Step 1: Understand the purpose of service boundaries

   Service boundaries should reflect business capabilities to ensure clear ownership and independent deployment.

2. Step 2: Evaluate the options

   Options B, C, and D focus on technical or team size factors, which are less effective than business-driven boundaries.

3. Final Answer:

   Divide the system based on business capabilities and data ownership -> Option D

4. Quick Check:

   Business capabilities = A [OK]

Hint: Match services to business functions, not code size or teams [OK]

Common Mistakes:

• Splitting services by code size only
• Grouping all database logic in one service
• Ignoring business domain boundaries

2. Which of the following is the correct way to define a microservice boundary?

easy

A. A service that handles user authentication and profile management

B. A service that mixes payment processing and product catalog updates

C. A service that only manages database connections

D. A service that handles logging for all other services

Solution

1. Step 1: Identify cohesive responsibilities

   A good service boundary groups related business functions, like authentication and profile management.

2. Step 2: Check for unrelated responsibilities

   Options A, B, and C mix unrelated concerns or are cross-cutting, which should be separate services or infrastructure.

3. Final Answer:

   A service that handles user authentication and profile management -> Option A

4. Quick Check:

   Cohesive business functions = D [OK]

Hint: Group related business tasks in one service [OK]

Common Mistakes:

• Combining unrelated business functions
• Creating services for technical concerns only
• Mixing cross-cutting concerns inside business services

3. Given a system with services: OrderService managing orders, InventoryService managing stock, and PaymentService handling payments, which service boundary violation is shown if OrderService directly updates stock quantities?

medium

A. OrderService is violating the single responsibility principle by managing inventory data

B. OrderService is correctly handling all order-related data including stock

C. PaymentService should update stock quantities instead

D. InventoryService should not exist separately from OrderService

Solution

1. Step 1: Analyze service responsibilities

   OrderService should focus on orders; InventoryService owns stock data and updates.

2. Step 2: Identify boundary violation

   OrderService updating stock breaks clear ownership and single responsibility principles.

3. Final Answer:

   OrderService is violating the single responsibility principle by managing inventory data -> Option A

4. Quick Check:

   Single responsibility violation = B [OK]

Hint: Each service owns its data; no direct updates outside boundaries [OK]

Common Mistakes:

• Allowing services to update data owned by others
• Confusing payment service role
• Merging unrelated services unnecessarily

4. A team notices that their UserService and NotificationService are tightly coupled because UserService calls NotificationService directly for every user update. What is the best way to fix this boundary issue?

medium

A. Make NotificationService call UserService instead

B. Merge both services into one to avoid communication

C. Use an event-driven approach where UserService emits events and NotificationService listens

D. Remove NotificationService and handle notifications inside UserService

Solution

1. Step 1: Understand tight coupling problem

   Direct calls create dependencies that reduce service independence.

2. Step 2: Apply event-driven design

   Emitting events decouples services, allowing independent scaling and deployment.

3. Final Answer:

   Use an event-driven approach where UserService emits events and NotificationService listens -> Option C

4. Quick Check:

   Event-driven decoupling = C [OK]

Hint: Use events to decouple services, not direct calls [OK]

Common Mistakes:

• Merging services unnecessarily
• Reversing call direction without decoupling
• Ignoring decoupling benefits

5. You are designing a microservices system for an e-commerce platform. Which approach best defines service boundaries to maximize team autonomy and scalability?

hard

A. Create services based on technical layers like UI, Business Logic, and Database Access

B. Define services around distinct business domains like Catalog, Orders, Payments, and Shipping, each owning its data and APIs

C. Split services by database tables regardless of business function

D. Group all user-related features into one large service to reduce communication

Solution

1. Step 1: Identify business domain boundaries

   Services aligned with business domains allow clear ownership and independent scaling.

2. Step 2: Avoid technical or data-layer splits

   Splitting by technical layers or tables causes tight coupling and reduces autonomy.

3. Step 3: Consider team autonomy and scalability

   Domain-based services enable teams to work independently and scale services as needed.

4. Final Answer:

   Define services around distinct business domains like Catalog, Orders, Payments, and Shipping, each owning its data and APIs -> Option B

5. Quick Check:

   Domain-driven design = A [OK]

Hint: Align services with business domains for autonomy and scale [OK]

Common Mistakes:

• Splitting by technical layers instead of business domains
• Grouping unrelated features together
• Ignoring data ownership in service design