You are designing a database strategy for a new web application. You plan to start with a small pilot in one country and eventually expand to millions of users in a global audience. You need to ensure that the application can run 24/7 with minimal downtime for maintenance. What should you do?

Cloud Spanner is the ideal choice for applications requiring high availability, strong consistency, and seamless scalability from regional to global. Starting with a regional configuration is a cost-effective approach for the initial pilot phase. This configuration provides a 99.99% availability SLA and supports zero-downtime maintenance and schema updates, fulfilling the 24/7 operational requirement. As the application expands globally, the Spanner instance can be seamlessly moved or reconfigured to a multi-region setup without requiring a complex migration, thus providing a clear and efficient growth path.

B. A multi-region configuration is premature and not cost-effective for the initial pilot, which is described as small and in one country.
C. Cloud SQL requires downtime for certain maintenance operations, such as major version upgrades, violating the minimal downtime requirement. It also doesn't scale writes horizontally for a global user base.
D. Highly available Cloud SQL is a regional solution. It does not address the future requirement to expand to a global audience and has the same maintenance downtime limitations as other Cloud SQL configurations.

1. Cloud Spanner Documentation - When to use Cloud Spanner: "Spanner is a good choice for... applications that have a global user base or have high availability requirements... Spanner offers up to 99.999% availability for multi-region instances, with no maintenance windows." This supports the choice of Spanner for high availability and global scale. The strategy starts regional and can grow to multi-region.

Source: Google Cloud Documentation, "When to use Cloud Spanner".

2. Cloud Spanner Documentation - Instances: "A regional configuration stores a full copy of your data in two zones within a single region... This configuration offers an availability of 99.99%." This validates that a regional start meets high availability needs for the pilot.

Source: Google Cloud Documentation, "Instances and configurations".

3. Cloud Spanner Documentation - Schema updates: "You can add or drop a column, add or drop an index, and add, drop, or alter a table without taking the database offline... Spanner schema updates do not require any downtime." This directly addresses the "minimal downtime for maintenance" requirement.

Source: Google Cloud Documentation, "Schema updates".

4. Cloud SQL Documentation - High Availability: "During a maintenance window, Cloud SQL HA instances are also subject to downtime." This confirms that Cloud SQL does not meet the minimal downtime requirement, making options C and D incorrect.

Source: Google Cloud Documentation, "High availability configuration".