When does user data run when provisioning an Amazon EC2 instance?

User data runs during the initial initialization phase of an Amazon EC2 instance, meaning it is executed after the instance has been launched and before it is ready for use. When an EC2 instance is started, the user data scripts can be set to perform tasks such as installing software, updating packages, or configuring settings that are essential for the instance's intended functions.

This initial initialization phase is crucial as it provides an opportunity to customize the instance at the moment of its first boot, ensuring that everything is set up correctly before the instance starts serving requests or performing its intended compute tasks.

Understanding this aspect of user data is essential for automating instance configurations in a cloud environment, as it allows for a streamlined setup process, particularly in scenarios involving scaling and repeated deployments.