https://www.oracle.com/assets/cloud-licensing-070579.pdf

For the purposes of licensing Oracle programs in an Authorized Cloud Environment, customers are required to count the maximum available vCPUs of an instance type as follows: 

Amazon EC2 and RDS – count two vCPUs as equivalent to one Oracle Processor license if multi-threading of processor cores is enabled, and one vCPU as equivalent to one Oracle Processor license if multi-threading of processor cores is not enabled. 

Microsoft Azure – count two vCPUs as equivalent to one Oracle Processor license if multithreading of processor cores is enabled, and one vCPU as equivalent to one Oracle Processor license if multi-threading of processor cores is not enabled.