For specific ec2 instance types the excess capacity is sometimes zero, which customers sometimes see. I've needed to swap instant types to get a deploy unstuck

For specific ec2 instance types the excess capacity is sometimes zero, which customers sometimes see. I've needed to swap instant types to get a deploy unstuck or to scale up in the past when capacity didn't exist. Because of that I always recommend that a project reserve instances to ensure capacity exists when you need it. It's also cheaper, but that risk is important to mitigate.