Region and Availability Zone Trivia

The same availability zones names in different AWS accounts could refer to different data centers, you need to check with AWS to get the right mapping between availability zone and physical data center

I was assuming that as long I am paying I shouldn't have constraints to the number of EC2 instances I could start, but it turns out that there are actual hard limits for the different services (not only EC2) and you will need to contact AWS to request a limit increase. This screenshot shows the screen were you can request limit increases for specific EC2 instance types.