AWS EBS Volume filling up even when the EC2 instance is stopped

Question

I received an AWS alert yesterday that the free-tier AWS EBS (gp2) volume on my account has reached 85% of the threshold limit.

I was confused to read that as I know for sure that the I did not start the EC2 instance that the EBS was attached to in a while.

I went and checked the CloudWatch metrics to see if the EC2 instance was up and running at any point in time in the last 2 weeks; but all the CloudWatch activity metrices showed up blank (which is what I expected).

For now I have de-attached and deleted the EBS volume because I did not want to incur any charges.

Is it possible that the EBS volume can bloat (in data size) even when the EC2 instance it is attached to has been shut-down all the while?

Answer 1

You pay for EBS storage independently of any instances that the storage is connected to.

The warning that you received is for EBS storage costs. 85% sounds about right given that this is the end of the month. Remember you pay for allocated space, not used space within the volume. So even if you add data to the volume every day, the cost will stay the same.

A common misperception is that if you stop an EC2 instance, there are no further charges. This is true for the EC2 instance itself (no charges) but other resources that you have allocated to the instance will continue to accrue charges. For example, static IP addresses, EBS storage, custom AMIs, snapshots, etc.

Is it possible that the EBS volume can bloat (in data size) even when the EC2 instance it is attached to has been shut-down all the while?

If an EC2 instance is shutdown or the EBS volume is detached, there will be no changes to the data on the volume. The volume will be exactly the same today, tomorrow, and next year.

Answer 2

You are charged for the amount of block storage you allocate, not the amount of data filling up that block storage

So turning off your EC2s will not stop the charge from incurring