I'm still stepping through SDfA, and I've reached a point of confusion between "ec2 instances" and "container instances". At this point, I've created an ECS cluster, and an EC2 instance. At this point in the course, it then asks me to verify that the "container instance" has joined the cluster. The list of container instances in the cluster is empty, but in the course they have one container. As far as I can tell, there was never a step to actually create a container instance, so I don't see how a container instance could have joined the cluster. Am I missing something, or did the course skip a step?