AWS VPC Peering: Free Data Transfer Within AZ & Costs Explained
Is seamless and cost-effective networking across your cloud infrastructure a priority? Understanding the nuances of Amazon Virtual Private Cloud (VPC) peering, particularly its cost implications, is crucial for optimizing your AWS spending and ensuring efficient data transfer.
VPC peering, a cornerstone of AWS networking, allows you to connect two VPCs, enabling traffic to flow between them using private IPv4 or IPv6 addresses. It's a direct connection, leveraging the existing infrastructure of a VPC, and does not require gateways, VPN connections, or physical hardware. This design contributes to its inherent resilience, as there's no single point of failure or bandwidth bottleneck.
| Feature | Details |
| Active VPC Peering Connections Per VPC | Yes (up to 125) |
| Outstanding VPC Peering Connection Requests | Unlimited |
| Expiry Time for an Unaccepted VPC Peering Connection Request | Not Specified. The connection request remains open until accepted or rejected. |
| Cost Components of VPC Peering | AWS charges for data transferred between VPCs over a peering connection when traffic crosses Availability Zones. There is no hourly fee for maintaining the peering connection, unlike Transit Gateway. |
| Data Transfer Within an Availability Zone | Free, as of May 1st, 2021 |
| Data Transfer Across Availability Zones | Incurs data transfer charges for ingress/egress traffic (see Figure 4 in AWS documentation for details) |
It's important to note the cost structure. Historically, data transfer across VPC peering connections incurred charges. However, a significant change came into effect on May 1st, 2021: data transfer over a VPC peering connection that stays within an Availability Zone (AZ) became free. This is a substantial cost-saving measure for organizations that design their applications and networks to keep data transfer within a single AZ.
However, the situation changes when data traverses Availability Zones. In these instances, data transfer charges are applied for ingress/egress traffic. These charges are based on the amount of data transferred, so understanding your application's data flow patterns is vital to cost management.
For instance, a customer planning VPC peering with different AWS accounts, all within the same region (e.g., Seoul), needs to be aware of the data transfer costs. If data transfer crosses AZs, the standard data transfer charges apply, which, in the example provided, are $0.01 USD/GB. The sender is responsible for data transfer costs, a fundamental principle of VPC peering.
This is in contrast to the AWS Transit Gateway, which offers a different networking architecture. While VPC peering is suitable for connecting a smaller number of VPCs within a region, Transit Gateway becomes more appropriate for larger, more complex network topologies that might involve multiple regions or a high volume of VPC connections.
Shared VPC configurations are another method for managing resources and networking in the cloud, offering an alternative approach to VPC peering. Shared VPC allows multiple AWS accounts to create and manage resources within a VPC owned by a central account, streamlining resource sharing and network management.
Furthermore, AWS also provides features such as advanced tier IPAM (IP Address Manager) and the use of VPC endpoints, to meet specific networking needs.
Lets delve into the specifics of the cost components and considerations for different scenarios of VPC peering, as this is a crucial aspect for the effective utilization of cloud resources.
Regarding hourly billing, it's worth mentioning that this also stops if the endpoint service owner rejects your VPC endpoint's attachment to their service, and that service is subsequently deleted.
In addition to these fundamental concepts, several practical considerations come into play. For instance, when establishing VPC peering, the AWS account ID and VPC ID fields contain the necessary information for making the peering request. Also, the CIDR block in use by the private space VPC, with which you'll be peering, is found in the AWS VPC CIDR field. The space CIDRs are the CIDR blocks from which your Dyno and ELB (Elastic Load Balancer) addresses are assigned.
It is important to note that VPC peering is not a gateway or VPN connection, meaning you won't need any separate hardware to establish the connection.
This architecture is both straightforward and flexible. When evaluating different network designs, it's important to consider your performance, compliance, and regulatory requirements.
Keep in mind, before setting up a VPC peering connection, you might need to create a request for approval, particularly if your internal policies require it. Also, data transfer between peered VPCs never traverses the public internet, increasing the security of the connection.
For the customer scenario, in the context of AWS VPC peering, who pays for the data transfer? The answer is that the account sending the data pays the data transfer charges. In a peered connection between Account A (VPC A) and Account B (VPC B), where all accounts are in the same AWS region (Seoul), if data transfer occurs, the account initiating the transfer will be responsible for the associated costs.
This holds true regardless of whether the data stays within a single Availability Zone (and is therefore free, as of May 1st, 2021) or crosses Availability Zones (and incurs standard data transfer charges).
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