When an instance pool scales in, in what order are instances terminated?

The correct answer focuses on the strategy used when terminating instances in an instance pool as it scales in. The process is designed to ensure stability and availability across different fault domains and availability domains.

When scaling in, instances are first balanced across availability domains, which helps maintain a consistent distribution of resources and prevents overloading any single domain. After this balancing, instances are then terminated based on their age. The idea here is to remove the oldest instances first, allowing for the newer instances to remain active, which might support a more up-to-date software version or configurations, enhancing overall system resilience.

This method of terminating instances not only helps maintain system performance but also simplifies recovery in case of failure, ensuring that the most recently updated instances can continue their operations while older ones are phased out systematically. This systematic approach aligns with best practices in cloud infrastructure management, emphasizing stability and reliability.