It sounds like EC2 is the foundation of the AWS Certified Developer - Associate and AWS Certified Solutions Architect - Associate exams. I am partial to the serverless technology, but EC2 and Auto Scaling Groups are pretty awesome.
I created a custom lab for myself that involves auto-scaling EC2 instances based on visible messages in an SQS Message Queue. The scenario is that I have a number of EC2 instances processing messages in a message queue. As the number of messages in the queue starts to increase or decrease the number of EC2 instances processing those messages is increased and decreased accordingly.
Cloudwatch monitors the message queue and sends alarms based on Queue Metrics - ApproximateNumberOfMessagesVisible. It sends the alarms to Auto Scaling Actions which scale-in and scale-out the number of EC2 instances!
I am amazed at how AWS Services are like logos and you can snap them together to build could stuff!