What is the difference between RunInstances:SV050 and RunInstances:SV051 in my Cost Explorer report?

I don't know if it's explained better elsewhere, but as hinted in https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/billing-info-fields.html, an "SV" designator shows the VPC Zone the instance is running in.

The RunInstances Operation for EC2 usage has additional detail codes separated by colons in the Cost and Usage Reports and subsequently Cost Explorer, as described be the documentation: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/billing-info-fields.html.

The first additional detail field, which is optional, describes the OS Platform. The full list of values are described in the documentation above, but for example:

• 0010 - Red Hat Enterprise Linux
• 1010 - Red Hat Enterprise Linux with HA
• 00g0 - Red Hat BYOL Linux For your example above, this field is not present - as indicated by the 'SV' at the start of the detail code. In this case, the Platform Details are "Linux/UNIX".

The second detail field, which is specified as starting with "SV", indicates Spot Instance-hour usage, along with the Availability Zone code (since Spot pricing is specific to an Availability Zone).

For your scenario, the usage for the first two operations maps to:

• Linux/UNIX Spot requests in AZ050
• Linux/UNIX Spot requests in AZ051

I'm not aware of any documentation that breaks down the values of these AZ codes further, however the Cost & Usage Report also includes the AZ mapped name in 'lineItem/AvailabilityZone' so if you need more information on what happened, you can consider evaluating your CUR (if setup).

In short, you can understand that there was a change in Spot usage between April 3rd & April 8th. As part of that Spot change, the workload change Availability Zone.