Compatibility Design Skill

Goal

To evolve systems without breaking existing users or downtime.

Capabilities

1. Database Migrations (Zero Downtime)

• Expand & Contract Pattern:
  1. Expand: Add new column/table. Sync data.
  2. Migrate: Code reads new, writes both.
  3. Contract: Remove old column.

2. API Versioning

• Strategies: URI Path (/v1/), Header (Accept-Version), Query Param.
• Tolerant Reader: Clients should ignore unknown fields (Forward Compatibility).

3. Feature Flags

• Decoupling: Launch != Deploy.
• Kill Switch: Turn off broken features instantly without rollback.