Defined in github.com/aws/aws-sdk-go/service/emr/api.go
To launch the job flow in Amazon VPC, set this parameter to the identifier of the Amazon VPC subnet where you want the job flow to launch. If you do not specify this value, the job flow is launched in the normal AWS cloud, outside of a VPC.
Amazon VPC currently does not support cluster compute quadruple extra large (cc1.4xlarge) instances. Thus, you cannot specify the cc1.4xlarge instance type for nodes of a job flow launched in a VPC.