DataTransfer-Regional-Bytes High Costs

InterZone-In and InterZone-Out are cross AZ data transfer costs. We often see this in containerized workloads when each POD is Multi-AZ, when the communication from 1 POD to another can cross AZs, then you can end up with this ping-pong type affect of traffic crossing back and forth between AZs. I suspect this is what you are seeing.

The only way I know of to limit this is to only have the Multi-AZ aspects of the workload at the ingress LB and the data store (DB?) and have each AZ deploy a set of PODs. This requires that the workload activity would be quick enough such that on a retry and timeouts if an AZ were to fail, the client would quickly try again and the next request would go to another AZ. You would still have some cross-AZ traffic at the LB and DB layers, but the POD to POD communications would all be in the same AZ.