High cohesion in Microservices - Architecture Diagram

System Overview - High cohesion

This system demonstrates high cohesion in a microservices architecture. Each microservice is focused on a single business capability, making the system easier to maintain and scale. The key requirement is to keep services independent and specialized for better reliability and development speed.

Architecture Diagram

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

Components

User

user

End user who sends requests to the system

Load Balancer

load_balancer

Distributes incoming user requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to appropriate microservices based on the request type

Order Service

service

Handles all order-related operations, focused on order management

Payment Service

service

Manages payment processing independently from other services

Inventory Service

service

Manages inventory data and stock levels separately

Order DB

database

Stores order data for the Order Service

Payment DB

database

Stores payment transaction data for the Payment Service

Inventory DB

database

Stores inventory information for the Inventory Service

Cache

cache

Speeds up read operations by caching frequently accessed data per service

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Order Service

Order Service → Cache

Cache → Order Service

Order Service → Order DB

Order DB → Order Service

Order Service → Cache

Order Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Order DB

Impact:Order Service cannot save new orders; reads may still succeed from cache but writes fail

Mitigation:Use database replication and failover to a standby DB; cache serves read requests temporarily

Architecture Quiz - 3 Questions

Which component directs user requests to the correct microservice?

A Load Balancer

B Cache

C API Gateway

D Database

Design Principle

This architecture shows high cohesion by assigning each microservice a single responsibility with its own database and cache. This separation reduces dependencies, making the system easier to maintain and scale.

Practice

1. What does high cohesion mean in microservices architecture?

easy

A. Using a single database for all microservices

B. Splitting every function into separate services regardless of relation

C. Combining unrelated tasks to reduce the number of services

D. Grouping related tasks and responsibilities within a single service

Solution

1. Step 1: Understand the meaning of cohesion

   Cohesion means how closely related the tasks inside a module or service are.

2. Step 2: Apply cohesion to microservices

   High cohesion means grouping related tasks in one service to keep it focused and manageable.

3. Final Answer:

   Grouping related tasks and responsibilities within a single service -> Option D

4. Quick Check:

   High cohesion = grouping related tasks [OK]

Hint: High cohesion means related tasks stay together [OK]

Common Mistakes:

• Thinking high cohesion means splitting every function separately
• Confusing cohesion with coupling
• Believing unrelated tasks should be combined
• Assuming database design defines cohesion

2. Which of the following is the correct way to describe a microservice with high cohesion?

easy

A. A service that manages all user-related operations like profile, login, and preferences

B. A service that mixes order processing and inventory updates randomly

C. A service that handles user authentication and payment processing

D. A service that only stores data without any business logic

Solution

1. Step 1: Identify related tasks in options

   A service that manages all user-related operations like profile, login, and preferences groups user-related operations which are closely related.

2. Step 2: Check other options for unrelated tasks

   Options A and B mix unrelated tasks; D lacks business logic, so not cohesive.

3. Final Answer:

   A service that manages all user-related operations like profile, login, and preferences -> Option A

4. Quick Check:

   High cohesion = related user tasks together [OK]

Hint: Look for grouping of related tasks in one service [OK]

Common Mistakes:

• Choosing options that mix unrelated responsibilities
• Ignoring business logic in cohesion
• Confusing data storage with service responsibility
• Assuming more tasks always mean better cohesion

3. Consider a microservice design where the OrderService handles order creation, payment processing, and shipping updates. What is the likely issue with this design regarding high cohesion?

medium

A. The service has low cohesion because it mixes unrelated responsibilities

B. The service has high cohesion because all tasks relate to orders

C. The service is scalable because it handles multiple tasks

D. The service is loosely coupled with other services

Solution

1. Step 1: Analyze the tasks in OrderService

   Order creation, payment, and shipping are different domains with distinct logic.

2. Step 2: Evaluate cohesion

   Mixing payment and shipping with order creation lowers cohesion because responsibilities differ.

3. Final Answer:

   The service has low cohesion because it mixes unrelated responsibilities -> Option A

4. Quick Check:

   Mixed tasks = low cohesion [OK]

Hint: Different domains in one service reduce cohesion [OK]

Common Mistakes:

• Assuming all order-related tasks are always cohesive
• Confusing scalability with cohesion
• Ignoring domain boundaries
• Believing loosely coupled means high cohesion

4. A microservice named InventoryService currently manages stock levels and supplier payments. What is the best fix to improve high cohesion?

medium

A. Combine InventoryService with OrderService

B. Add customer order tracking to InventoryService

C. Split supplier payments into a separate PaymentService

D. Keep all tasks in InventoryService for simplicity

Solution

1. Step 1: Identify unrelated responsibilities

   Supplier payments are unrelated to stock level management.

2. Step 2: Suggest separation for high cohesion

   Moving payments to a dedicated PaymentService improves cohesion by grouping related tasks.

3. Final Answer:

   Split supplier payments into a separate PaymentService -> Option C

4. Quick Check:

   Separate unrelated tasks to improve cohesion [OK]

Hint: Separate unrelated tasks into different services [OK]

Common Mistakes:

• Adding unrelated tasks to the same service
• Combining unrelated services
• Ignoring cohesion for simplicity
• Confusing cohesion with coupling

5. You are designing a microservices system for an e-commerce platform. To ensure high cohesion, which of the following service groupings is best?

hard

A. UserService (user profiles, payments), OrderService (orders, shipping), InventoryService (stock levels, payments)

B. UserService (user profiles, authentication), OrderService (orders, payments), ShippingService (shipping updates, tracking)

C. One big service handling users, orders, payments, shipping, and inventory

D. Split every function into its own microservice regardless of relation

Solution

1. Step 1: Evaluate grouping of related tasks

   UserService (user profiles, authentication), OrderService (orders, payments), ShippingService (shipping updates, tracking) groups related tasks logically by domain, supporting high cohesion.

2. Step 2: Compare with other options

   UserService (user profiles, payments), OrderService (orders, shipping), InventoryService (stock levels, payments) mixes payments in unrelated services; C is a monolith; D over-splits causing low cohesion.

3. Final Answer:

   UserService (user profiles, authentication), OrderService (orders, payments), ShippingService (shipping updates, tracking) -> Option B

4. Quick Check:

   Group related domain tasks for high cohesion [OK]

Hint: Group by domain responsibilities for high cohesion [OK]

Common Mistakes:

• Mixing unrelated tasks in one service
• Creating too many tiny services
• Building monolithic services
• Ignoring domain boundaries