public void setDefaultSubnetId(String defaultSubnetId) {
        this.defaultSubnetId = defaultSubnetId;
    }
<p>
The stack's default VPC subnet ID. This parameter is required if you specify a value for the <code>VpcId</code>
parameter. All instances are launched into this subnet unless you specify otherwise when you create the instance.
If you also specify a value for <code>DefaultAvailabilityZone</code>, the subnet must be in that zone. For
information on default values and when this parameter is required, see the <code>VpcId</code> parameter
description.
</p>

@param defaultSubnetId
       The stack's default VPC subnet ID. This parameter is required if you specify a value for the
       <code>VpcId</code> parameter. All instances are launched into this subnet unless you specify otherwise
       when you create the instance. If you also specify a value for <code>DefaultAvailabilityZone</code>, the
       subnet must be in that zone. For information on default values and when this parameter is required, see
       the <code>VpcId</code> parameter description.
aws-java-sdk-opsworks/src/main/java/com/amazonaws/services/opsworks/model/CreateStackRequest.java