Comment by 22c | Hacker News Reader

Comment by 22c | Hacker News Reader

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Except the entire premise is not true...

I am not sure what Corey has done to get to these numbers, but inter-AZ traffic within the same VPC is free.

Perhaps the problem is that the pricing page is very confusing [1].

Probably the confusing part is that VPC peering between one VPC and another that crosses an AZ is not free, but you do not need to do that to compete with RDS availability.

> The problem that I want to highlight today is that if I spin up MySQL myself on EC2 instances, I’ll have to pay 2¢ per GB that I replicate between AZs, whereas I will pay nothing if I use RDS.

This sentence specifically, is not true. If your EC2 instances are in the same VPC but different AZs the data transfer is still free.

There's a better blog post which explains what is and isn't free here [2].

[1] https://aws.amazon.com/ec2/pricing/on-demand/

[2] https://aws.amazon.com/blogs/architecture/overview-of-data-t...

I can tell you from experience of optimizing those bills that it’s very much NOT free in the same vpc for inter-az traffic.

From the link you provided:

> Data transferred between a Local Zone and an Availability Zone within the same AWS Region, “in” to and “out” from Amazon EC2 in the Local Zone Pricing Data transfer in $0.01 Data transfer out $0.01

A Local Zone is not the same as an Availability Zone, a Local Zone is an edge computing location.

Hm actually you’re right about this one (and the fact it’s confusing af) but they do charge you for cross-az traffic as anyone who tried to run reasonably loaded multi-az kafka cluster will attest to

> This sentence specifically, is not true. If your EC2 instances are in the same VPC but different AZs the data transfer is still free.

Your assertion is not true. We run intra-VPC services across AZs and they are billed for network traffic. It's also shown as incurring cost in your second source.

I had made this same comment then deleted it in order to check for sure. You are right that the Amazon docs are horribly confusing. The pricing page is up there with the descriptions of security on S3.

This diagram within your source 2 seems to directly contradict what you're saying: https://d2908q01vomqb2.cloudfront.net/fc074d501302eb2b93e255...

This diagram from a third party suggests that the traffic between different AZs in the same region is "No cost", but the written text suggests otherwise.

https://www.cloudbolt.io/guide-to-aws-cost-optimization/aws-...

Granted it is a third party website.

I wonder if something has changed with their pricing.

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