API versioning for services in Microservices - Architecture Diagram

System Overview - API versioning for services

This system manages multiple versions of APIs for microservices to ensure backward compatibility and smooth upgrades. It allows clients to specify which API version they want to use, enabling gradual migration and minimizing disruptions.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway (Version Router)
  |               |               |
  v               v               v
Service v1      Service v2      Service v3
  |               |               |
  v               v               v
Database       Database       Database
  ^               ^               ^
  |               |               |
Cache           Cache           Cache

Components

User

client

Sends API requests specifying desired version

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway (Version Router)

api_gateway

Routes requests to the correct service version based on API version in request

Service v1

service

Handles API requests for version 1

Service v2

service

Handles API requests for version 2

Service v3

service

Handles API requests for version 3

Database

database

Stores persistent data for each service version

Cache

cache

Speeds up data retrieval for each service version

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway (Version Router)

API Gateway (Version Router) → Service vX (based on version)

Service vX → Cache

Cache → Service vX

Service vX → Database

Database → Service vX

Service vX → Cache

Service vX → API Gateway (Version Router)

API Gateway (Version Router) → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:API Gateway (Version Router)

Impact:All API requests fail to route to service versions, causing complete service outage.

Mitigation:Deploy multiple API Gateway instances behind the load balancer for redundancy and failover.

Architecture Quiz - 3 Questions

Which component decides which service version handles the API request?

A API Gateway (Version Router)

B Load Balancer

C Cache

D Database

Design Principle

This architecture uses an API Gateway as a version router to direct client requests to the correct microservice version. This enables multiple API versions to coexist, supporting backward compatibility and smooth upgrades without disrupting users.

Practice

1. What is the main purpose of API versioning in microservices?

easy

A. To increase server hardware requirements

B. To improve database performance

C. To reduce network latency

D. To allow changes without breaking existing clients

Solution

1. Step 1: Understand API versioning goal

   API versioning is used to manage changes in APIs so that old clients still work without errors.

2. Step 2: Identify the main benefit

   This helps avoid breaking existing users when new features or fixes are added.

3. Final Answer:

   To allow changes without breaking existing clients -> Option D

4. Quick Check:

   API versioning = avoid breaking changes [OK]

Hint: API versioning prevents breaking old clients [OK]

Common Mistakes:

• Thinking it improves database speed
• Confusing it with network optimization
• Assuming it increases hardware needs

2. Which of the following is a common way to specify API version in a request?

easy

A. Using the URL path like /v1/resource

B. Embedding version in the database schema

C. Changing the server IP address

D. Using client-side cookies only

Solution

1. Step 1: Identify common API versioning methods

   API versions are often specified in the URL path, headers, or query parameters.

2. Step 2: Match the correct method

   Using the URL path like /v1/resource is a widely used and clear approach.

3. Final Answer:

   Using the URL path like /v1/resource -> Option A

4. Quick Check:

   URL path versioning = Using the URL path like /v1/resource [OK]

Hint: Version in URL path is common and clear [OK]

Common Mistakes:

• Confusing version with database schema
• Thinking server IP changes version
• Assuming cookies control API version

3. Given a microservice with two API versions running side by side, what happens when a client sends a request to /api/v2/users?

medium

A. The service processes the request using version 1 logic

B. The service returns an error because version 2 is unsupported

C. The service processes the request using version 2 logic

D. The service ignores the version and uses the latest version

Solution

1. Step 1: Understand version routing

   When multiple API versions run side by side, the version in the URL directs which logic to use.

2. Step 2: Match URL version to service logic

   A request to /api/v2/users should be handled by version 2 logic, not version 1 or latest by default.

3. Final Answer:

   The service processes the request using version 2 logic -> Option C

4. Quick Check:

   URL version directs logic = The service processes the request using version 2 logic [OK]

Hint: URL version selects matching service logic [OK]

Common Mistakes:

• Assuming version 1 logic runs always
• Thinking unsupported versions cause errors
• Believing latest version is default without version

4. A developer tries to version an API by changing the request header to X-API-Version: 3, but clients still get version 1 responses. What is the likely issue?

medium

A. The client is sending the wrong URL path

B. The service does not support header-based versioning

C. The server is down

D. The database schema is outdated

Solution

1. Step 1: Analyze versioning method mismatch

   If clients send version info in headers but the service expects URL path versioning, the header is ignored.

2. Step 2: Identify the cause of version mismatch

   The service likely does not support header-based versioning, so it defaults to version 1 responses.

3. Final Answer:

   The service does not support header-based versioning -> Option B

4. Quick Check:

   Unsupported header versioning = The service does not support header-based versioning [OK]

Hint: Check if service supports header versioning [OK]

Common Mistakes:

• Blaming wrong URL when header is used
• Assuming server down causes version mismatch
• Confusing database schema with API version

5. You need to design a microservice API that supports smooth migration from version 1 to version 2 without downtime. Which approach best supports this?

hard

A. Run both versions side by side and route requests based on URL version

B. Replace version 1 completely with version 2 immediately

C. Use only query parameters for versioning and ignore URL paths

D. Deploy version 2 on a different server without routing

Solution

1. Step 1: Understand smooth migration needs

   Smooth migration requires both versions to run simultaneously so clients can switch gradually.

2. Step 2: Choose routing strategy

   Routing requests based on URL version allows clients to specify which version they want, enabling coexistence.

3. Step 3: Evaluate other options

   Replacing immediately causes downtime; query-only versioning is less clear; separate servers without routing complicate access.

4. Final Answer:

   Run both versions side by side and route requests based on URL version -> Option A

5. Quick Check:

   Side-by-side versioning = Run both versions side by side and route requests based on URL version [OK]

Hint: Run versions side by side for smooth migration [OK]

Common Mistakes:

• Replacing old version immediately causing downtime
• Ignoring URL path versioning clarity
• Deploying without routing causing access issues