Aurora reader storage cost
that should be simple, but I cannot figure that out
Amazon bills the real used storage amount for Aurora databases, not the allocated storage like for non-Aurora.
there is a metric VolumeBytesUsed - The amount of storage used by your Aurora DB instance. This metric applies to an entire Aurora DB cluster, not for instance. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Aurora.Monitoring.html
I have a cluster of 1 Arora Writer and 2 Readers. DB size is about 10 Gb and VolumeBytesUsed shows 10Gb. According to documentation, each Aurora node has its own data copy - https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Aurora.Overview.html So if I have 10Gb DB - Aurora Writer and 2 Readers should be using 10x3 = 30 Gb of storage, but VolumeBytesUsed shows 10Gb
Will I be billed for 10 Gb or 30 Gb in that case?
From the Aurora MySQL FAQ, which I found linked from the pricing page.
Q: Amazon Aurora replicates each chunk of my database volume six ways across three Availability Zones. Does that mean that my effective storage price will be three or six times what is shown on the pricing page?
No. Amazon Aurora’s replication is bundled into the price. You are charged based on the storage your database consumes at the database layer, not the storage consumed in Amazon Aurora’s virtualized storage layer.
Based on what I know about AWS (quite a bit) and what I've read (not a lot) I think each database is charged once for storage. That means if you have a 10GB database service with two 10GB read replicas you'll be charged for 30GB of storage.
here is what I got from support:
Aurora by design, is managed in a clustered format. Both writer and reader instances of aurora cluster are associated with same storage layer hence there will not be any extra charge for storage when you provision additional reader instance. The charges to aurora cluster are calculated on a cluster level so if you have one writer and one (or more) reader instance, you will be charged as below:
Cost of DB instances (if you have one writer and one reader, you will be charged for two instances)
Total storage on cluster level
Total IO consumed on cluster level
Charges for backtrack feature (if applicable)
Charges for Snapshot export (if applicable)
Charges for cross-AZ data transfer in same region (if applicable)