API Design & Maintenance: Scenario-Based Questions

Backward compatibility ensures that older clients keep working even as the API evolves. It's essential in systems where clients can’t upgrade immediately or where uptime is critical.

🔑 What Is Backward Compatibility?

• Existing clients can continue functioning without code changes.
• Newer versions may add features, but not break old ones.

🧱 Strategies for Backward-Compatible APIs

• Versioning: Use URL paths (e.g., /v1/users) or headers (Accept: application/vnd.api+json;version=2).
• Additive Changes Only: Add fields but never remove or rename them.
• Deprecation Notices: Warn consumers of upcoming changes.
• Default Behavior: Maintain default values if new fields are missing.

📊 Techniques by API Type

• REST: Version via route or media type; avoid breaking changes in schema.
• GraphQL: Use deprecated fields and avoid schema deletions until safe.
• gRPC: Protocol Buffers support backward compatibility by default if you follow field numbering rules.

✅ Best Practices

• Test older clients against newer API versions (contract testing).
• Document version lifecycle policies clearly.
• Automate schema diff checks in CI/CD pipelines.
• Communicate deprecation early and often.

🚫 Common Pitfalls

• Renaming or removing fields without notice.
• Changing data formats (e.g., timestamp strings → epoch ints).
• No documentation of API changes or client impact.

📌 Final Insight

Designing backward-compatible APIs earns user trust and operational stability. Be additive, explicit, and consistent — and always think like your downstream clients.