What practice contributes to zero-downtime migrations in practice?

What practice contributes to zero-downtime migrations in practice?

• A. Use backward-compatible schema changes and application-side readiness
• B. Schedule migrations during peak hours only
• C. Skip backups to save time
• D. Replace entire database instead of migrating

Answer: (A)

Using backward-compatible schema changes and application-side readiness is the practice that makes zero-downtime migrations possible. The idea is to change the database in a way that the old code can still operate while the new code is phased in. This often means adding new columns or tables instead of renaming or dropping existing ones, making fields nullable or providing defaults so existing queries keep working, and introducing feature flags or routing logic to shift traffic to the new behavior gradually. Data migrations can run in the background or in small chunks, and there should be a clear rollback path if issues arise. Scheduling migrations during peak hours doesn’t guarantee zero downtime and still risks disruption. Skipping backups is unsafe and can lead to data loss in case something goes wrong. Replacing the entire database would typically require downtime and data reconciliation, which defeats the goal of zero downtime.

Using backward-compatible schema changes and application-side readiness is the practice that makes zero-downtime migrations possible. The idea is to change the database in a way that the old code can still operate while the new code is phased in. This often means adding new columns or tables instead of renaming or dropping existing ones, making fields nullable or providing defaults so existing queries keep working, and introducing feature flags or routing logic to shift traffic to the new behavior gradually. Data migrations can run in the background or in small chunks, and there should be a clear rollback path if issues arise.

Scheduling migrations during peak hours doesn’t guarantee zero downtime and still risks disruption. Skipping backups is unsafe and can lead to data loss in case something goes wrong. Replacing the entire database would typically require downtime and data reconciliation, which defeats the goal of zero downtime.