Final answer:
Autoscaling in Oracle Cloud Infrastructure (OCI) compute is the feature that meets the requirements to adjust application capacity automatically based on demand, ensure high availability, and optimize costs.
Step-by-step explanation:
To automatically match capacity to demand and keep the application always up and running while saving costs, the appropriate Oracle Cloud Infrastructure (OCI) compute feature to use is Autoscaling. Autoscaling allows you to automatically adjust the number of compute instances in an instance pool based on performance metrics such as CPU utilization or network I/O. The autoscaling policy can be set up to increase the instance count during peak traffic times, such as weekends for this application, and decrease it during off-peak times, ensuring that you are only paying for the resources your app actually needs. Moreover, because it's automatic, it removes the need for manual intervention and helps maintain the application's availability even during unexpected surges in demand. Additionally, using combinations of autoscaling policies and scheduling, you can fine-tune the resources to match predictable traffic patterns to optimize costs further.