Why each service owns its data in Microservices - Architecture Impact

System Overview - Why each service owns its data

This system shows a microservices architecture where each service manages its own database. This means no two services share the same data storage. The key goal is to keep services independent, scalable, and easy to maintain.

Each service owns its data to avoid tight coupling and to allow teams to work independently without conflicts.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  +----------------+----------------+----------------+
  |                |                |
Service A       Service B        Service C
  |                |                |
Database A     Database B       Database C
  |                |                |
Cache A        Cache B          Cache C

Components

User

client

Sends 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 specific business logic and owns Database A

Service B

service

Handles different business logic and owns Database B

Service C

service

Handles another business domain and owns Database C

Database A

database

Stores data exclusively for Service A

Database B

database

Stores data exclusively for Service B

Database C

database

Stores data exclusively for Service C

Cache A

cache

Speeds up data access for Service A

Cache B

cache

Speeds up data access for Service B

Cache C

cache

Speeds up data access for Service C

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Service A

Service A → Cache A

Cache A → Service A

Service A → Database A

Database A → Service A

Service A → Cache A

Service A → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Database A

Impact:Service A cannot write or read fresh data; cache may serve stale data

Mitigation:Use database replication for failover; cache serves stale reads; alert team for repair

Architecture Quiz - 3 Questions

Why does each service have its own database?

A To make the system slower

B To keep services independent and avoid data conflicts

C To share data easily between services

D To reduce the number of databases

Design Principle

This architecture shows the principle of data ownership in microservices. Each service manages its own database to stay independent, avoid conflicts, and allow teams to develop and scale services separately. This reduces tight coupling and improves system resilience.

Practice

1. Why should each microservice own its own data instead of sharing a common database?

easy

A. To ensure services are independent and can evolve separately

B. To reduce the total amount of data stored in the system

C. To make it easier to write SQL queries across services

D. To allow all services to access data faster by sharing it

Solution

1. Step 1: Understand service independence

   Each microservice owning its data means it can change its database without affecting others.

2. Step 2: Recognize benefits of separate data ownership

   This independence improves scalability and reduces tight coupling between services.

3. Final Answer:

   To ensure services are independent and can evolve separately -> Option A

4. Quick Check:

   Service independence = D [OK]

Hint: Think about service independence and avoiding tight coupling [OK]

Common Mistakes:

• Assuming shared databases improve performance
• Believing data sharing reduces storage needs
• Thinking SQL queries are easier with shared data

2. Which of the following is the correct way for microservices to access data owned by another service?

easy

A. Directly querying the other service's database

B. Sharing a common database schema

C. Using APIs or messaging to request data

D. Copying the entire database locally

Solution

1. Step 1: Identify proper data access method

   Microservices should not access each other's databases directly to avoid tight coupling.

2. Step 2: Recognize communication via APIs or messages

   Services communicate data through APIs or messaging systems to maintain independence.

3. Final Answer:

   Using APIs or messaging to request data -> Option C

4. Quick Check:

   Data access via APIs/messages = B [OK]

Hint: Remember: no direct DB access, use APIs or messages [OK]

Common Mistakes:

• Trying to query another service's database directly
• Assuming shared schema is best practice
• Copying entire databases unnecessarily

3. Consider two microservices: Service A owns customer data, and Service B owns order data. Service B needs customer info to process orders. Which approach correctly respects data ownership?

medium

A. Service B queries Service A's database directly for customer info

B. Service B calls Service A's API to get customer info

C. Service B duplicates customer data in its own database

D. Service B uses a shared database for both customer and order data

Solution

1. Step 1: Identify correct data access respecting ownership

   Service B should not access Service A's database directly or share databases.

2. Step 2: Use API calls for data retrieval

   Calling Service A's API allows Service B to get needed data without breaking ownership rules.

3. Final Answer:

   Service B calls Service A's API to get customer info -> Option B

4. Quick Check:

   API calls respect ownership = A [OK]

Hint: Use APIs to get data from other services, not direct DB access [OK]

Common Mistakes:

• Direct DB queries across services
• Duplicating data causing inconsistency
• Using shared databases breaking independence

4. A team notices that two microservices share a database schema and directly query each other's tables. What is the main problem with this design?

medium

A. It causes tight coupling and reduces service independence

B. It improves scalability by sharing data

C. It simplifies API design between services

D. It reduces the need for data synchronization

Solution

1. Step 1: Analyze impact of shared database schema

   Sharing schema and direct queries create tight coupling between services.

2. Step 2: Understand consequences on independence

   Tight coupling reduces the ability to change or scale services independently.

3. Final Answer:

   It causes tight coupling and reduces service independence -> Option A

4. Quick Check:

   Tight coupling problem = C [OK]

Hint: Shared DB means tight coupling, which is bad for microservices [OK]

Common Mistakes:

• Thinking shared DB improves scalability
• Assuming it simplifies API design
• Believing it removes sync needs

5. You are designing a microservices system with three services: User, Inventory, and Order. Each service owns its data. How should you handle a scenario where the Order service needs to confirm inventory availability before placing an order?

hard

A. All services share a single database to simplify data access

B. Order service queries Inventory service's database directly to check stock

C. Order service duplicates inventory data locally and updates it periodically

D. Order service calls Inventory service's API to check stock availability

Solution

1. Step 1: Respect data ownership in design

   Each service must own and manage its own data; direct DB queries or shared DB break this.

2. Step 2: Use API calls for inter-service communication

   Order service should call Inventory service's API to get real-time stock info, ensuring data consistency and independence.

3. Final Answer:

   Order service calls Inventory service's API to check stock availability -> Option D

4. Quick Check:

   API communication respects ownership = A [OK]

Hint: Always use APIs for cross-service data, never direct DB access [OK]

Common Mistakes:

• Direct DB queries breaking independence
• Duplicating data causing stale info
• Using shared DB increasing coupling