The virtual machines (or sub vApps) will be started in the order specified in the vApp configuration. If the vApp is suspended (@see vim.VirtualApp.Summary.suspended), all suspended virtual machines will be powered-on based on the defined start-up order.
While a vApp is starting, all power operations performed on sub entities are disabled through the VIM API. They will throw TaskInProgress.
In case of a failure to power-on a virtual machine, the exception from the virtual machine power on is returned, and the power-on sequence will be terminated. In case of a failure, virtual machines that are already started will remain powered-on.