Where the charges come from
| Traffic | Charged? | Notes |
|---|---|---|
| Into AWS from the internet | No | |
| Out of AWS to the internet | Yes, per GB | AWS includes a monthly free allowance across services |
| Between Availability Zones in a region | Yes, in both directions | Each gigabyte is charged when it leaves one zone and again when it arrives in the other |
| Within one Availability Zone, over private IPs | Usually no | |
| Between regions | Yes, per GB | |
| Through a NAT Gateway | Yes, a processing charge per GB | On top of any transfer charge. See NAT Gateway costs. |
| From an AWS origin to CloudFront | No | You pay for CloudFront’s delivery to viewers instead |
The patterns behind a big bill
Chatty services spread across zones
Spreading services across Availability Zones is right for resilience, but a service that makes many calls to another service in a different zone pays for every gigabyte twice. Keep the heaviest conversations in the same zone where you can, for example by routing to zone-local replicas or instances.
Serving files straight from S3 or a load balancer
Put CloudFront in front. Transfer from an AWS origin to CloudFront is free, and CloudFront caches repeated downloads close to users.
Replicating data between regions
Cross-region replication, backups and disaster-recovery copies all transfer data. Check they copy what you need, as often as you need it, and nothing more.
Private traffic going the long way
Workloads that reach S3 or DynamoDB through a NAT Gateway pay transfer and processing charges that a free gateway endpoint would avoid.
Finding it in the bill
- In Cost Explorer, filter the service to EC2 (where most transfer charges land) and group by usage type. Transfer usage types include
DataTransferin their names, and NAT processing includesNatGateway. - Look at regional transfer (between zones) separately from transfer out to the internet. They have different causes and different fixes.
- For the biggest line, use VPC Flow Logs to find which workloads send the traffic and where it goes.
Sources
- AWS: Amazon VPC pricing
- AWS: Amazon CloudFront pricing
- AWS: price reduction for data transfer out to the internet
See also Lower cloud costs.
Next step
Not sure where your data transfer comes from?
On a 30-minute call we’ll look at your bill and point to the traffic behind it.