A database migration runs through a private network path, but the migration service cannot connect although the source is healthy. Which approach best fits?

1. Plan conversion and validation of incompatible schema and application logic.
2. Validate the service's required routing, firewall, DNS, and database access settings.
3. Define rollback criteria, data reconciliation, and source-retention procedures before cutover.
4. Add supported change synchronization or schedule an approved write freeze.