I will provide a very high level of what the VMware VIX API is, since there is a awesome presentation by Matt LaMantia at TechExchange in VMworld 2010 SF that goes into more details about VIX (video below). The VIX API (Virtual Infrastructure eXtension) is an API that provides guest management operations inside of a virtual machine that maybe running on VMware vSphere, Fusion, Workstation or Player. These operations are executed on behalf of the vmware-tools service that must be running within the virtual machine and guest credentials are required prior to execution.
The current incarnation of the VIX API is a little odd because it provides guest management operations which is unique to the VIX API but it also provides virtual machine operations. These virtual machine operation overlaps with some of the functionality provided by the vSphere API which is used for managing your vSphere infrastructure. Part of this overlap was due to origins of VIX which started from Workstation on the desktop. I almost consider this VMware API sprawl :)
There are several ways of using the VIX API today. If you are using PowerCLI, there are actually a few cmdlets that directly integrate with VIX, which requires you to install the VIX client libraries local to your PowerCLI installation. One such cmdlet is the Invoke-VMScript and here are a few example use cases:
VGC (Virtual Guest Console) created by the VMware Lab guys also known as flings. This is a graphical interface similar to VMware Remote Console, but it is 1000x better and provides integration to all the VIX operations. The application allows you to view running processes in a guest, kill a particular process, deploy application to a guest, download/upload files and browse guest filesystem and much much more. I would highly recommend taking a look at this tool!
As you can see, the possibilities are endless! but you still have to use two separate APIs. I along with others in the community have asked for a consolidation of the VIX API and merging with the vSphere API, makes the most sense. I think our feedback has finally been heard and if you watch the presentation given by Matt, you will see that future of VIX API is exactly that, consolidatation with the vSphere API. Though we will not see it anytime soon until the next major release of vSphere dubbed vSphere.next (MN) and vSphere.next^2 (OP), it is a change I am looking forward to.
In the VIX 1.6.2 release, you actually have full VIX read and write operations against an ESXi host using the free license. This was of course fixed in subsequent releases and the trick only works with ESXi 4.0 or older. You will notice on the VIX landing page, there is no mention of the release notes for 1.6.2 release other than 1.7.1 superseding it. You however still can download 1.6.2 release under VIX 1.6 and you can still see the release notes if you search on VMware's site or on Google.
PPC15 Guest Operations Using VMware VIX APIs and Beyond:
Guest Operations using VMware VIX APIs and Beyond from heyitspablo on Vimeo.