The quiet $0.01/GB each way that multi-AZ high availability costs you.
Spreading services across zones bills roughly $0.02/GB round trip — invisible until it is thousands of dollars. Keep chatter in-zone. See the wider-scope cost on the inter-region transfer calculator and Kafka impact on the managed Kafka calculator.
Free cross-AZ transfer cost calculator — GB moved between availability zones to the round-trip cost of multi-AZ HA.
On AWS, traffic between availability zones is charged at about $0.01/GB for egress out of the source AZ and again for ingress into the destination — roughly $0.02/GB round trip. Chatty services split across zones pay this on every message.
Use zone-aware routing so services talk within their own AZ where possible, read from same-zone replicas (fetch-from-follower in Kafka), and weigh single-AZ deployments for workloads that do not need multi-AZ durability. HA is worth it, but design to minimize cross-zone chatter.
Cost at different volumes:
| Volume | Monthly | Yearly |
|---|