Data Transfer Charges

Question

Consider my AWS infrastructure is like this

I have my database hosted and running on a EC2 machine and also my application is also running on different EC2 machine and another application on another EC2 machine in total 3 EC2 machine 
One for database and remaining two for applications.

So when I search for datatransfer changers in AWS I got results like
There will only charges incur in case sending data outside of AWS cloud and for incoming data there will no charges
So according to above line considering my setup only one application in my setup sends data outside of the cloud remaining database and another application sends data to the application which is sending data outside of the cloud. So here only charges incur in case of my one application sending data out side of the cloud is that right.

Sending Out (Egress): Charges applied
Receiving Data (Ingress): Free with no restriction

If wrong please correct me

Riku_Kobayashi · Accepted Answer

Hello.

I think your understanding is correct because outbound communication to the internet incurs charges.  
This means that you are charged for the applications that communicate over the Internet.  
By the way, if the database server and application server are running in different availability zones, charges will also be incurred for the portion between the database and the application.  
Communication within the same availability zone is free.  
https://aws.amazon.com/ec2/pricing/on-demand/?nc1=h_ls  
> Data transferred between Amazon EC2, Amazon RDS, Amazon Redshift, Amazon ElastiCache instances, and Elastic Network Interfaces in the same Availability Zone is free.

Clarence · Answer

Your understanding is correct, you get charged for Outbound Traffic (out of AWS) but not charged for Inbound traffic (coming in to AWS). 
Note for outbound AWS offers 100 GB of free data transfer out to the internet each month. This applies to all AWS services and regions, except China and GovCloud.

Other points to take note of:
- Per the previous post you need to be aware of inter AZ if your DB & Application are in communicating across AZ's there is dta transfer charges
- If your DB and Applications are in different regions there is a Interregion Data Transfer cost
- If your resrouces (EC2 instances) are communicating with each other using public/elastic IP addresses there is both incoming/outgoing data charge.

This blog provides a comprehensive view of data transfer charges.
https://aws.amazon.com/blogs/architecture/overview-of-data-transfer-costs-for-common-architectures/

Data Transfer Charges

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