AWS Certified Solutions Architect Associate Test 2

Best Practices for Configuring Elastic Network Interfaces
You can attach an elastic network interface to an instance when it's running (hot attach), when it's stopped (warm attach), or when the instance is being launched (cold attach).
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#best-practices-for-configuring-network-interfaces