Final answer:
In cloud computing, alerts or alarms trigger autoscaling events. They are configured to respond to specific performance metrics, automatically adjusting the number of service instances based on the load.
Step-by-step explanation:
The cloud feature that triggers autoscaling events is alerts or alarms. In cloud environments like AWS, Azure, and GCP, autoscaling is typically configured to respond to certain performance metrics that indicate the need to adjust the number of instances of a service. When a predefined threshold is crossed, an alert or alarm is triggered, prompting the autoscaling mechanism to either launch additional instances to handle increased load or terminate some instances to scale down.