Shared database anti-pattern in Microservices - Architecture Diagram

System Overview - Shared database anti-pattern

This system shows a microservices architecture where multiple services directly access the same database. This is called the shared database anti-pattern. It causes tight coupling between services and can lead to data conflicts and scaling problems.

The key requirement is to understand why sharing a database among microservices is problematic and how it affects system reliability and scalability.

Architecture Diagram

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

Components

User

user

End user who 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

Microservice handling a specific business domain

Service B

service

Another microservice handling a different business domain

Service C

service

Third microservice handling another business domain

Shared Database

database

Single database accessed directly by all microservices

Cache Layer

cache

Caches frequently accessed data to reduce database load

Request Flow - 9 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Service A

Service A → Shared Database

Shared Database → Cache Layer

Service B → Shared Database

Service B → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Shared Database

Impact:All microservices lose access to data, causing system-wide failures. Writes and reads fail, leading to downtime and inconsistent data state.

Mitigation:Implement database replication and failover to a standby database. Use service-level caching to serve stale data during outages. Consider decoupling services with separate databases to reduce impact.

Architecture Quiz - 3 Questions

Why is sharing a single database among microservices considered an anti-pattern?

A It improves data consistency and reduces latency

B It creates tight coupling and data conflicts between services

C It allows services to scale independently

D It simplifies service deployment

Design Principle

This architecture demonstrates the shared database anti-pattern where multiple microservices tightly couple by accessing the same database. This leads to scaling challenges, data conflicts, and single points of failure. Proper microservices design favors database per service to ensure loose coupling and independent scalability.

Practice

1. What is the main problem caused by the shared database anti-pattern in microservices?

easy

A. Better fault isolation between services

B. Tight coupling between services due to shared data schema

C. Easier scaling of individual services

D. Improved performance by sharing data directly

Solution

1. Step 1: Understand the shared database anti-pattern

   This anti-pattern happens when multiple microservices use the same database schema directly.

2. Step 2: Identify the impact on service independence

   Sharing the database causes tight coupling, making services dependent on each other's data structure changes.

3. Final Answer:

   Tight coupling between services due to shared data schema -> Option B

4. Quick Check:

   Shared database = Tight coupling [OK]

Hint: Shared DB means tight coupling, breaking microservices independence [OK]

Common Mistakes:

• Thinking shared DB improves scaling
• Assuming shared DB isolates faults
• Believing shared DB simplifies service design

2. Which of the following is the correct way to avoid the shared database anti-pattern in microservices?

easy

A. Use a single database schema shared by all services

B. Store all data in a centralized monolithic database

C. Allow direct SQL queries from one service to another's database

D. Each service owns its own database and communicates via APIs

Solution

1. Step 1: Recall best practice for microservice data management

   Each microservice should have its own database to maintain independence.

2. Step 2: Identify the correct communication method

   Services communicate through APIs, not by sharing databases or direct queries.

3. Final Answer:

   Each service owns its own database and communicates via APIs -> Option D

4. Quick Check:

   Separate DB + APIs = Avoid shared DB anti-pattern [OK]

Hint: Separate DB per service + API calls avoid shared DB anti-pattern [OK]

Common Mistakes:

• Choosing shared schema for simplicity
• Allowing direct cross-service DB queries
• Centralizing all data in one DB

3. Consider two microservices, Service A and Service B, sharing the same database. Service A changes a table schema without informing Service B. What is the most likely outcome?

medium

A. Service B automatically adapts to the new schema

B. Service B continues working without issues

C. Service B experiences runtime errors due to schema mismatch

D. Both services improve performance

Solution

1. Step 1: Analyze the impact of schema change on shared DB

   When services share a database, schema changes affect all services using it.

2. Step 2: Predict Service B's behavior

   Service B expects the old schema; a change causes runtime errors like failed queries or crashes.

3. Final Answer:

   Service B experiences runtime errors due to schema mismatch -> Option C

4. Quick Check:

   Schema change + shared DB = runtime errors [OK]

Hint: Schema change in shared DB breaks other services [OK]

Common Mistakes:

• Assuming automatic schema adaptation
• Believing no impact on other services
• Thinking performance improves

4. You find that two microservices share a database causing tight coupling and deployment issues. Which change fixes this problem?

medium

A. Create separate databases and add API communication

B. Merge the two services into one monolith

C. Add more indexes to the shared database

D. Allow both services to write to the same tables

Solution

1. Step 1: Identify the root cause of tight coupling

   Sharing the same database schema causes deployment and coupling problems.

2. Step 2: Apply the correct fix

   Separating databases and using APIs decouples services and allows independent deployment.

3. Final Answer:

   Create separate databases and add API communication -> Option A

4. Quick Check:

   Separate DB + APIs fix shared DB anti-pattern [OK]

Hint: Separate DB + APIs fix tight coupling from shared DB [OK]

Common Mistakes:

• Merging services loses microservice benefits
• Adding indexes doesn't fix coupling
• Allowing shared writes keeps tight coupling

5. A company has three microservices sharing one database. They want to migrate to avoid the shared database anti-pattern. Which approach best balances data consistency and service independence?

hard

A. Split databases per service and use event-driven messaging for data sync

B. Keep shared database but add strict schema versioning

C. Merge all services into a single database schema with shared tables

D. Use direct SQL queries between services to keep data consistent

Solution

1. Step 1: Understand the trade-offs in migration

   Separating databases improves independence but can cause data consistency challenges.

2. Step 2: Choose a pattern that balances consistency and independence

   Event-driven messaging allows services to sync data asynchronously while keeping separate databases.

3. Final Answer:

   Split databases per service and use event-driven messaging for data sync -> Option A

4. Quick Check:

   Separate DB + events balance consistency and independence [OK]

Hint: Use separate DB + events for sync to avoid shared DB anti-pattern [OK]

Common Mistakes:

• Keeping shared DB limits independence
• Merging services loses microservice benefits
• Using direct SQL breaks service boundaries