2 | Availability zones (AZs) are distinct geographical locations that are engineered to be insulated from failure in other AZs. By placing Amazon EC2 instances in multiple AZs, an application can be protected from failure at a single location. It is important to run independent application stacks in more than one AZ, either in the same region or in another region, so that if one zone fails, the application in the other zone can continue to run. When you design such a system, you will need a good understanding of zone dependencies. |