Can I assume that my availability zone us-east-1a is the same location as someone else's availability zone us-east-1a?

No. Currently, we do not support cross-account proximity. Each account's availability zones are independent. There is no assurance that your availability zone us-east-1a will be the same as any other account's availability zone us-east-1a.

How can I make sure that I am in the same availability zone as another developer?

We do not currently support the ability to coordinate availability groups between developer accounts. We are seeking customer feedback to understand the types of use cases for proximity control between accounts. We will use this feedback to determine how and when we can provide availability zone control between accounts.

Regional data transfer seems like such a small charge, why are you complicating my bill with this?

We anticipate that for most common use cases, regional data transfer will only constitute a very small portion of your monthly usage charges. There are valid use cases that involve moving large amounts of data between availability zones. In these cases, the regional data transfer can be a significant cost.

We try to enable as many use cases as possible while charging you only for what you use. Because of the large potential differences in the way developers will use regional data transfer, we think it is appropriate to break this cost out rather than amortize it across other charges.

If I have two instances in different availability zones, how will I be charged for regional data transfer?

Each instance is charged for its data in and data out. Therefore, if data is transferred between these two instances, it is charged out for the first instance and in for the second instance.

If I transfer data between availability zones using public IP addresses, will I be charged twice for Regional Data Transfer (once because it’s across zones, and a second time because I'm using public IP addresses)?

No. Regional Data Transfer rates apply if at least one of the following is true, but is only charged once for a given instance even if both are true: