API versioning strategies in HLD - System Design Guide

Problem Statement

When an API evolves, clients using older versions may break due to incompatible changes. Without a clear versioning strategy, it becomes impossible to maintain backward compatibility, causing service disruptions and forcing all clients to upgrade simultaneously.

Solution

API versioning strategies allow multiple versions of an API to coexist, enabling clients to choose which version to use. This is done by embedding version information in the URL path, request headers, or query parameters, so servers can route requests to the correct version implementation without breaking existing clients.

Architecture

Client v1

→API Gateway

↓

Client v2

→API Gateway

This diagram shows clients using different API versions routed through an API Gateway to the corresponding service version implementations.

Trade-offs

✓ Pros

→

Allows backward compatibility by supporting multiple API versions simultaneously.

→

Enables gradual client migration to newer API versions without service disruption.

→

Improves API lifecycle management by isolating changes to specific versions.

✗ Cons

→

Increases maintenance overhead as multiple API versions must be supported and tested.

→

Can cause confusion if versioning strategy is inconsistent or poorly documented.

→

May lead to code duplication or complexity in service implementations.

Use when your API undergoes breaking changes and you have multiple clients that cannot upgrade simultaneously, especially at scale above hundreds of clients.

Avoid if your API is stable with no breaking changes expected or if you control all clients and can enforce simultaneous upgrades.

Real World Examples

Amazon

Uses URL path versioning (e.g., /v1/, /v2/) to maintain backward compatibility for its AWS APIs while rolling out new features.

Stripe

Uses header-based versioning to allow clients to specify API version in request headers, enabling smooth upgrades without changing URLs.

GitHub

Supports media type versioning where clients specify API version in the Accept header, allowing flexible version negotiation.

Alternatives

No versioning

No explicit versioning; all clients use the same API endpoint and must adapt to changes immediately.

Use when: Only when you control all clients and can guarantee simultaneous updates without breaking changes.

Feature toggles

Use feature flags to enable or disable new API features without changing the API version.

Use when: When changes are additive and backward compatible, avoiding the need for multiple versions.

Summary

API versioning prevents client breakage by allowing multiple API versions to coexist.

Common strategies include URL path, headers, and query parameters to specify versions.

Choosing the right versioning approach depends on client control, scale, and change frequency.

Practice

1. Which of the following is a common method to implement API versioning?

easy

A. Changing the database schema without notice

B. Including the version number in the URL path

C. Using random query parameters unrelated to version

D. Ignoring backward compatibility

Solution

1. Step 1: Understand common API versioning methods

   API versioning often uses clear, explicit methods like URL paths, query parameters, or headers to indicate version.

2. Step 2: Evaluate options for correctness

   Only including the version number in the URL path is a standard, clear method. Other options either break compatibility or are unrelated.

3. Final Answer:

   Including the version number in the URL path -> Option B

4. Quick Check:

   Version in URL path = B [OK]

Hint: Version in URL path is the most visible method [OK]

Common Mistakes:

• Confusing random query parameters with versioning
• Ignoring backward compatibility importance
• Assuming database changes equal API versioning

2. Which syntax correctly shows versioning using a query parameter in an API request?

easy

A. GET /api/resource?v=2

B. GET /api/v2/resource

C. GET /api/resource/version2

D. GET /api/resource?version-2

Solution

1. Step 1: Identify query parameter versioning syntax

   Query parameter versioning appends a key-value pair like ?v=2 to the URL.

2. Step 2: Compare options for correct query parameter format

   GET /api/resource?v=2 uses ?v=2 which is correct. Others use path or invalid query syntax.

3. Final Answer:

   GET /api/resource?v=2 -> Option A

4. Quick Check:

   Query param version = C [OK]

Hint: Query params use ?key=value format [OK]

Common Mistakes:

• Using path segments instead of query parameters
• Incorrect query parameter syntax like missing '='
• Confusing version in path with query versioning

3. Given this API Gateway routing rule: if request.header['API-Version'] == 'v2' then route to service_v2 else route to service_v1, what happens when a request has no API-Version header?

medium

A. Request is rejected with error

B. Request is routed to service_v2

C. Request is routed to service_v1

D. Request is routed randomly

Solution

1. Step 1: Analyze the routing condition

   The rule routes to service_v2 only if header 'API-Version' equals 'v2'. Otherwise, it routes to service_v1.

2. Step 2: Determine routing when header is missing

   If the header is missing, condition fails, so request goes to service_v1 by default.

3. Final Answer:

   Request is routed to service_v1 -> Option C

4. Quick Check:

   Missing header defaults to v1 routing = A [OK]

Hint: Missing header triggers else branch routing [OK]

Common Mistakes:

• Assuming missing header routes to v2
• Thinking missing header causes error
• Believing routing is random without header

4. A developer implemented API versioning by adding a new version in the URL path but forgot to update the API Gateway routing rules. What is the most likely problem?

medium

A. The old version will be disabled automatically

B. All requests will be routed correctly to the new version

C. API Gateway will automatically detect and route new versions

D. Requests to the new version will fail or go to the old service

Solution

1. Step 1: Understand API Gateway role in version routing

   API Gateway must be configured to route requests to correct service versions based on URL or headers.

2. Step 2: Analyze impact of missing routing update

   If routing rules are not updated for new URL version, requests won't reach the new service and may fail or default to old service.

3. Final Answer:

   Requests to the new version will fail or go to the old service -> Option D

4. Quick Check:

   Missing routing update causes failures = A [OK]

Hint: Update routing rules with new version URLs [OK]

Common Mistakes:

• Assuming API Gateway auto-updates routing
• Believing old version disables automatically
• Ignoring routing configuration importance

5. You need to design an API that supports multiple versions simultaneously without breaking existing clients. Which strategy best supports this requirement?

hard

A. Use an API Gateway to route requests based on version in headers or URL

B. Change the API contract directly and remove old versions immediately

C. Use only query parameters for versioning and ignore headers

D. Deploy a single service that handles all versions internally without routing

Solution

1. Step 1: Identify requirements for supporting multiple versions

   Supporting multiple versions simultaneously requires clear routing to different service versions without breaking clients.

2. Step 2: Evaluate strategies for version management

   Using an API Gateway to route requests based on version in headers or URL cleanly separates versions and maintains backward compatibility.

3. Step 3: Eliminate less scalable or risky options

   Removing old versions immediately breaks clients; relying only on query parameters limits flexibility; single service handling all versions complicates code and risks errors.

4. Final Answer:

   Use an API Gateway to route requests based on version in headers or URL -> Option A

5. Quick Check:

   API Gateway routing supports multiple versions = D [OK]

Hint: API Gateway routing is key for multi-version support [OK]

Common Mistakes:

• Removing old versions too soon
• Ignoring header-based versioning
• Overloading single service with all versions