aws_vpc_peering_connection cost estimation

An aws_vpc_peering_connection is a direct, private network link between two VPCs so resources can talk over private IPs without a transit gateway, VPN, or internet gateway. Unlike a transit gateway, a peering connection has no hourly attachment fee. Creating and accepting the peering is free.

The cost is entirely the data transfer that flows across it. For peering between VPCs in the same region, traffic is billed like cross-AZ transfer: about $0.01/GB in each direction when it crosses an Availability Zone boundary, and free when both endpoints are in the same AZ. For inter-region peering, traffic is billed at inter-region data transfer rates, typically in the $0.02/GB range depending on the regions, and it applies to traffic in both directions. High-volume replication or chatty microservices across a peering can therefore add up even though the connection line item is zero.

Because there is no hourly fee, the optimization is about placement and volume: keep peered traffic same-AZ where possible to avoid the cross-AZ charge, and prefer same-region peering over inter-region when the architecture allows. c3x prices the cross-AZ and inter-region transfer that flows over a peering connection and treats the connection itself as free.

Terraform example

A minimal but realistic configuration that C3X can estimate.

resource "aws_vpc_peering_connection" "app_to_data" {
  vpc_id      = aws_vpc.app.id
  peer_vpc_id = aws_vpc.data.id
  auto_accept = true

  tags = {
    Name = "app-to-data"
  }
}

Pricing dimensions

What you actually pay for when you provision aws_vpc_peering_connection.

Dimension	Unit	What's being charged
Peering connection	free	The connection has no creation fee and no hourly charge. $0
Same-region data transfer	per GB	Traffic across the peering that crosses an AZ boundary is billed both ways; same-AZ traffic is free. $0.01/GB each way (cross-AZ)
Inter-region data transfer	per GB	Traffic over inter-region peering is billed at inter-region rates in both directions. ~$0.02/GB depending on regions

Optimization tips

Common ways to reduce aws_vpc_peering_connection cost without changing the workload.

Keep peered traffic in the same AZ

Removes cross-AZ transfer on peered traffic

Same-region peering is free within an AZ but $0.01/GB each way across AZs. Align workloads that talk over peering to the same Availability Zone to avoid the charge.

Prefer same-region over inter-region peering

Inter-region peering carries the higher inter-region transfer rate on every byte both ways. Keep peered VPCs in one region unless latency or residency requires otherwise.

Consolidate many peerings onto a transit gateway only when justified

A transit gateway simplifies a mesh of peerings but adds hourly attachment and per-GB processing fees. For a few connections, free peering is cheaper.

FAQ

Does a VPC peering connection cost money?

The connection itself is free with no hourly charge. You pay only for the data transfer that crosses it: cross-AZ rates within a region, or inter-region rates between regions.

Is VPC peering cheaper than a transit gateway?

For a small number of VPCs, yes. Peering has no hourly fee, while a transit gateway adds an hourly attachment charge plus per-GB processing on top of transfer. A large mesh may still favor a transit gateway for manageability.

How do I reduce VPC peering costs?

Keep chatty peered workloads in the same Availability Zone to avoid the $0.01/GB cross-AZ charge, and prefer same-region peering over inter-region to avoid the higher inter-region transfer rate.