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To design a system I need to decide on where to deploy the instances (suppose that I don't really care where they are but only want to optimize costs).

The on-demand page mentions several billing items:

  1. Data Transfer IN To Amazon EC2 From Internet
  2. Data Transfer OUT From Amazon EC2 To Internet
  3. Data Transfer OUT From Amazon EC2 To (a list of regions)
  4. Data Transfer Across AZ within this Region

My questions:

  • About item 1 - they say this is free, is it? does it make sense that from Internet to Amazon is free while from Amazon to Amazon is not free? (I'm talking on the inbound data here, not the outbound).
  • In items 2-3: does "Amazon" refer to all AWS services, including another EC2 instance?
  • Regarding item 4: it is written "Data transferred "in" to and "out" of Amazon EC2, Amazon RDS, Amazon Redshift , Amazon DynamoDB Accelerator (DAX), and Amazon ElastiCache instances or Elastic Network Interfaces across VPC peering connections in the same AWS region is charged at $0.01/GB." Is that meaning that if I run a process between 2 EC2 instances on the same region then I pay for each GB twice? first for outbound from one instance and second for the inbound on the other instance.
Bush
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    I'm voting to close this question as off-topic because this isn't AWS support – jonrsharpe Jul 28 '18 at 15:04
  • reason I posted here is that I found other question on this topic on SO, like https://stackoverflow.com/questions/33149584/difference-between-data-transfer-cost-and-bandwidth-costs-in-aws and more – Bush Jul 28 '18 at 15:15
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    There are numerous articles and even training classes for understanding AWS pricing. I recommend "studying" those instead of asking for opinions. – John Hanley Jul 28 '18 at 17:28
  • There are numerous articles and even training classes for understanding almost everything discussed on this website. I didn't ask for an opinion. – Bush Jul 28 '18 at 17:36
  • But opinion is all you will get here. You need an authoritative and enforceable answer. Your linked question is also off topic. – user207421 Jul 29 '18 at 00:35

1 Answers1

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The simple rules-of-thumb are:

  • Inbound traffic from the Internet to the AWS Cloud is free.
  • Outbound traffic from the AWS Cloud to the Internet is charged at the applicable rates in each region (this is the majority of the cost). This applies to anything that sends traffic out to the Internet from your AWS services.
  • Outbound traffic from the AWS Cloud to Amazon CloudFront has a lesser rate
  • Traffic within a region but between Availability Zones is 1c/GB in each direction. In fact, the wording on the EC2 Instance Pricing page now shows this.

To answer your specific questions:

  • Inbound is free
  • Outbound is for any AWS service that sends traffic to the Internet
  • Traffic between AZs or via VPC Peering is charged in "each direction"
John Rotenstein
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  • Thank you! Just to clarify on the 3rd question: If 2 instances send 1GB to one another then my overall cost would be COST_PER_GB times 4? or times 2? – Bush Jul 29 '18 at 07:12
  • From my reading, it would seem that if an instance in AZ-1 sends 1GB to an instance in AZ-2, then you would be charged 1GB _out_ and 1GB _in_, for a total of 2c. If the instance sent an equivalent amount back, it would be 4c. (2GB in + 2GB out.) – John Rotenstein Jul 29 '18 at 09:10