Managing Breaking Changes

Even with versioning, you need a strategy for introducing breaking changes gracefully. Let's learn how to manage API evolution.

Deprecation Process

1. Announce Deprecation

Communicate through:

• API responses (headers)
• Documentation
• Email to developers
• Changelog

2. Set Deprecation Timeline

Announcement ─► Grace Period ─► Sunset ─► Removal
    Day 1         6 months       Day X      Day X+30

3. Add Deprecation Headers

HTTP/1.1 200 OK
Deprecation: true
Sunset: Sat, 01 Jul 2025 00:00:00 GMT
Link: <https://api.example.com/v2/users>; rel="successor-version"

Strategies for Breaking Changes

1. Field Aliasing

Support both old and new field names:

// v1 response (old field)
{ "username": "alice" }

// Transition: return both
{ "username": "alice", "userName": "alice" }

// v2 response (new field only)
{ "userName": "alice" }

2. Response Expansion

Add new fields without removing old ones:

// v1
{ "name": "Alice Smith" }

// v2 (expanded, backward compatible)
{
  "name": "Alice Smith",
  "firstName": "Alice",
  "lastName": "Smith"
}

3. Feature Flags

Enable new behavior opt-in:

GET /api/users
X-Enable-New-Response: true

Exercise: Backward Compatible Response

Communication Best Practices

Documentation

## Deprecated Endpoints

### GET /api/v1/users (Deprecated)
**Sunset date**: July 1, 2025
**Replacement**: GET /api/v2/users

Migration guide: [Link to guide]

Changelog

## 2024-01-15

### Deprecated
- `GET /v1/users` - Use `GET /v2/users` instead
- `name` field - Use `firstName` and `lastName`

### Removed
- `GET /v0/legacy` - Sunset reached

Response Headers

Warning: 299 - "This endpoint is deprecated. Use /v2/users"

Migration Checklist

1. Analyze impact - Which clients use deprecated features?
2. Create migration guide - Step-by-step instructions
3. Announce with timeline - Give adequate notice
4. Add deprecation warnings - In responses and docs
5. Monitor usage - Track deprecated endpoint calls
6. Support migration - Help clients transition
7. Remove when safe - After sunset date

Summary

Managing breaking changes:

• Communicate early and often
• Use deprecation headers
• Support backward compatibility when possible
• Provide clear migration paths
• Give adequate transition time