Anti-corruption layer in Microservices - Architecture Diagram

System Overview - Anti-corruption layer

An Anti-corruption Layer (ACL) is a design pattern used in microservices to protect a service from changes or complexity in another service's model. It acts as a translator or adapter, ensuring that the internal system remains clean and consistent while interacting with external or legacy systems.

Key requirements include isolating the internal domain model, translating data formats, and preventing direct dependency on external service models.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Internal Service <---> Anti-Corruption Layer <---> External Service
                             |
                             v
                        External Database

Components

User

client

Initiates requests to the system

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Handles client requests, routing them to internal services

Internal Service

service

Core business logic service with its own clean domain model

Anti-Corruption Layer

adapter_service

Translates and adapts data and commands between internal service and external service

External Service

external_service

Legacy or third-party service with a different domain model

External Database

database

Data storage used by the external service

Request Flow - 12 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Internal Service

Internal Service → Anti-Corruption Layer

Anti-Corruption Layer → External Service

External Service → External Database

External Database → External Service

External Service → Anti-Corruption Layer

Anti-Corruption Layer → Internal Service

Internal Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Anti-Corruption Layer

Impact:Internal service cannot communicate with external service, causing failures or stale data for features relying on external data.

Mitigation:Implement fallback mechanisms such as cached data or default responses; monitor ACL health and use circuit breakers to prevent cascading failures.

Architecture Quiz - 3 Questions

What is the main purpose of the Anti-Corruption Layer in this architecture?

A To balance load between API Gateway instances

B To translate and adapt data between internal and external services

C To store user session data

D To directly expose the external database to users

Design Principle

The Anti-Corruption Layer pattern helps maintain a clean and stable internal domain model by isolating it from external systems with different models. This reduces complexity and dependency risks, enabling easier maintenance and evolution of the internal service.

Practice

1. What is the main purpose of an Anti-corruption layer in microservices architecture?

easy

A. To translate and isolate differences between two systems to prevent corruption

B. To speed up database queries between microservices

C. To store user session data securely

D. To monitor network traffic between services

Solution

1. Step 1: Understand the role of the anti-corruption layer

   The anti-corruption layer acts as a translator between two systems with different models or rules.

2. Step 2: Identify its main goal

   Its goal is to prevent the internal system from being affected or corrupted by external system differences.

3. Final Answer:

   To translate and isolate differences between two systems to prevent corruption -> Option A

4. Quick Check:

   Anti-corruption layer = Translation and isolation [OK]

Hint: Think: 'translator' between systems to avoid confusion [OK]

Common Mistakes:

• Confusing it with caching or monitoring layers
• Thinking it speeds up queries directly
• Assuming it stores user data

2. Which of the following is the correct way to implement an anti-corruption layer between two microservices?

easy

A. Directly expose the legacy system's database schema to the new service

B. Allow the new system to write directly to the legacy system's tables

C. Use the same data model in both systems without changes

D. Create a translation interface that maps legacy data to the new system's model

Solution

1. Step 1: Review implementation best practices

   An anti-corruption layer should translate and map data between systems, not share schemas directly.

2. Step 2: Identify the correct approach

   Creating a translation interface that maps legacy data to the new system's model isolates differences and protects both systems.

3. Final Answer:

   Create a translation interface that maps legacy data to the new system's model -> Option D

4. Quick Check:

   Translation interface = Correct implementation [OK]

Hint: Map legacy data to new model, never share schemas directly [OK]

Common Mistakes:

• Exposing legacy database schema directly
• Using identical data models without translation
• Allowing direct writes to legacy tables

3. Given the following pseudo-code for an anti-corruption layer translating legacy user data, what will be the output?

legacyUser = {"fullName": "Jane Doe", "age": 30}

function translateUser(legacy) {
  return {
    name: legacy.fullName,
    isAdult: legacy.age >= 18
  }
}

newUser = translateUser(legacyUser)
console.log(newUser)

medium

A. {"name": "Jane Doe", "isAdult": false}

B. {"fullName": "Jane Doe", "isAdult": true}

C. {"name": "Jane Doe", "isAdult": true}

D. {"name": "Jane Doe"}

Solution

1. Step 1: Analyze the translation function

   The function creates a new object with 'name' from 'fullName' and 'isAdult' as true if age >= 18.

2. Step 2: Apply the function to the legacy user

   legacyUser has fullName 'Jane Doe' and age 30, so isAdult is true.

3. Final Answer:

   {"name": "Jane Doe", "isAdult": true} -> Option C

4. Quick Check:

   Translate fullName and check age >= 18 = true [OK]

Hint: Check property mapping and age condition carefully [OK]

Common Mistakes:

• Using legacy property names in output
• Incorrectly evaluating age condition
• Missing one of the output properties

4. A developer wrote this anti-corruption layer code snippet but it causes errors when legacy data is missing some fields:

function translateOrder(legacyOrder) {
  return {
    id: legacyOrder.orderId,
    total: legacyOrder.amount.value,
    status: legacyOrder.status.toUpperCase()
  }
}

What is the main issue and how to fix it?

medium

A. The function should return legacyOrder directly without changes

B. The code assumes nested fields exist; add checks to handle missing or undefined fields

C. Use lowercase for status instead of toUpperCase()

D. Remove the id field to avoid errors

Solution

1. Step 1: Identify the error cause

   The code accesses nested fields like legacyOrder.amount.value without checking if amount exists, causing errors if missing.

2. Step 2: Fix by adding safety checks

   Use conditional checks or optional chaining to safely access nested fields and avoid runtime errors.

3. Final Answer:

   The code assumes nested fields exist; add checks to handle missing or undefined fields -> Option B

4. Quick Check:

   Missing field checks cause errors = add safety checks [OK]

Hint: Always check nested fields exist before accessing [OK]

Common Mistakes:

• Ignoring null or undefined nested objects
• Returning legacy data without translation
• Changing case without reason
• Removing necessary fields

5. You need to integrate a legacy billing system with your new microservice. The legacy system uses different currency codes and date formats. How should you design the anti-corruption layer to handle this integration effectively?

hard

A. Build a translation layer that converts legacy currency codes to standard ISO codes and normalizes date formats before passing data to the new service

B. Modify the legacy system to use the new system's currency codes and date formats directly

C. Ignore currency and date differences and pass data as-is to the new service

D. Store all legacy data in the new system without any translation

Solution

1. Step 1: Identify integration challenges

   Legacy system uses different currency codes and date formats, which can cause data misinterpretation.

2. Step 2: Design translation in anti-corruption layer

   Create a layer that converts legacy currency codes to standard ISO codes and normalizes date formats to the new system's expected format.

3. Final Answer:

   Build a translation layer that converts legacy currency codes to standard ISO codes and normalizes date formats before passing data to the new service -> Option A

4. Quick Check:

   Translate legacy formats to standard before integration [OK]

Hint: Translate legacy formats to standard before integration [OK]

Common Mistakes:

• Trying to change legacy system directly
• Passing data without translation
• Storing legacy data without normalization