AWS Data Transfer charges when using Heroku Rails app with Amazon RDS backend

Question

I have a Ruby on Rails app hosted on Heroku that has a PostgreSQL database that I have hosted outside of Heroku, in my own AWS account as an RDS instance. So Heroku manages my compute/app, and AWS directly manages my RDS. (The reason for this is because the cost is lower than buying the database on Heroku.) However, on my AWS bill, in addition to the RDS charges, I am seeing Data Transfer charges for bandwidth in the us-east-1 region. Heroku's EC2 instances and my RDS instance are both in the same us-east-1 region. I am wondering why I am seeing these Data Transfer charges, and if there is a way to mitigate them without having to stop using Heroku? Thanks in advance.

Answer 1

If your instances / services are located in the same region but in different availability zones, there will be data transfer charges. This is called a regional data transfer and is charged $.01 per GB. There are variations and exceptions. Best to consult Amazon's web site to determine your exact pricing.

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