Connect to the ESXi host containing the virtual machine targeted for backup. 
A side-effect of this step is determining the arrangement and description of virtual machines on the host.

Tell the host to take a snapshot of the target virtual machine, using the vSphere API. Use the quiesce flag, but not the memory flag, which is incompatible with quiesce. The virtual machine continues to run, while the snapshot provides a static (quiesced) view.

Capture the virtual disk data and virtual machine configuration information (vim.vm.ConfigInfo).

On the ESXi host, use the VDDK (programming in C or C++) to open and read the virtual disk and snapshot files. Copy them to backup media, along with configuration information.

Tell the host to delete the backup snapshot, using the vSphere API.