When building a modern, high-performant application at scale, it’s important to make sure the individual application instances are distributed across a variety of data centers. For cloud based applications, this means multiple availability zones. Putting your application in multiple availability zones increases your availability and resiliency.
However, if your application uses multiple AWS accounts, your multi-AZ application may not be as resilient as you think. In fact, two services running in two different AZs, may in fact actually be running on the same physical servers!
To understand why, you need to understand how the availability zone abstraction works. This episode discusses this abstraction and how you can keep your applications safe and resilient.