What feature of Azure SQL Database allows for automatic scaling?

Azure SQL Database offers a feature known as Elastic Pools that enables automatic scaling. This feature is particularly beneficial for organizations that need to manage multiple databases with varying usage patterns. Elastic Pools allow databases to share a set amount of resources, such as CPU and memory, and this resource management facilitates the automatic scaling of resources across databases within the pool based on their workloads.

When databases in an Elastic Pool require more resources due to increased demand—such as during peak operational times—they can dynamically take advantage of the pool's capabilities. This flexibility helps to maintain performance without the need for manual intervention to adjust resource allocation for individual databases, making it more efficient and cost-effective. Since you're charged based on the provisioned resources of the pool rather than each individual database, this can also lead to significant cost savings.

The other options do not offer the same level of automatic scaling capabilities with respect to resource management. SQL Managed Instance provides features conducive to enterprise-level needs but lacks the same level of resource pooling and elasticity. Geo-Replication focuses on disaster recovery and ensuring availability across regions, while long-term retention relates to data backup rather than scaling resources. Thus, Elastic Pools stands out as the correct choice for enabling automatic scaling in Azure SQL Database.