Describes the specified attribute of the specified instance. You can specify only one attribute at a time. Valid attribute values are: <code>instanceType</code> | <code>kernel</code> | <code>ramdisk</code> | <code>userData</code> | <code>disableApiTermination</code> | <code>instanceInitiatedShutdownBehavior</code> | <code>rootDeviceName</code> | <code>blockDeviceMapping</code> | <code>productCodes</code> | <code>sourceDestCheck</code> | <code>groupSet</code> | <code>ebsOptimized</code> | <code>sriovNetSupport</code>