Difference between free tier GP2 storage and gp2 storage running PostgreSQL?

Hello, I hope you are doing well! From your question, its unclear the region in which your resources are operating and if you are running PostgreSQL within Amazon EC2 or if you are leveraging Amazon RDS to run your database. For each service, there is separate free tier which stipulates what you will not be charged for as long as you are operating within the free tier limits.

For example, Amazon EBS when used with Amazon EC2 allows for the following utilization within the free tier (link to source):

• 30 GB of Amazon EBS: any combination of General Purpose (SSD) or Magnetic
• 2,000,000 I/Os (with EBS Magnetic)
• 1 GB of snapshot storage

With Amazon RDS, the free tier includes the following usage (link to source):

• 750 Hours per month of db.t2.micro database usage (applicable DB engines)
• 20 GB of General Purpose (SSD) database storage
• 20 GB of storage for database backups and DB Snapshots

**Note that the RDS free tier is inclusive of its storage utilization whereas EC2 and EBS have separate free tiers. **

Moving forward, I suggest you leverage AWS Cost Explorer to further dive into your AWS utilization and costs. If you are using RDS, I suggest specifying the following within Cost Explorer:

• Group By - Usage Type
• Filter - Service - Relational Database Service
• Filter - Usage Type Group - RDS: Storage

If you are using EC2, I suggest specifying the following within Cost Explorer:

• Group By - Usage Type
• Filter - Service - EC2-Other
• Filter - Usage Type Group - EC2: EBS - SSD(gp2)

For either of the above views in Cost Explorer, you'll be able to see the volume usage in GB-Month as well as any associated costs for that utilization. I hope that this answers your question and provides additional visibility into why you were seeing costs for gp2.