Working with the vCenter Server Simulator 5.5 – configuring custom ESXi hosts

Working with VCSIM (vCenter Server Simulator)


William Lam has done some excellent blog posts on using the simulator included with the VCSA (vCenter Server Appliance), to setup a simulated vSphere environment. Just the other day at VMworld Europe, he presented a session for vBrownBag entitled “NotSupported Tips/Tricks for vSphere 5.5“. In this session he introduced the new simulator, he dubs “VCSIM 2.0”, which is the latest iteration included with the VCSA 5.5 appliance.

I had previously had a brief look at the VCSIM included with 5.1, but after seeing its limited functionality, did not pursue its use for development testing. However, after learning about the features introduced in VCSIM “2.0”, I just had to take a further look…

To see how to setup and start VCSIM, have a read of Will’s blog post here. However, at a high level, this is what you need to do to start the simulator with defaults:

  • Deploy and fully configure the VCSA 5.5 appliance. Make sure DNS (forward and reverse) is working and the embedded database is properly configured, otherwise the vpxa service will have trouble intialising
  • Ensure you have no issues with the embedded DB being reset (i.e. don’t do this on a production VCSA!)
  • SSH in to the appliance
  • issue command: vmware-vcsim-start default


Customising the default VCSIM ESXi host model


Today, I needed to replicate a certain condition in our lab environment. Specifically, I needed the ESXi hosts to have 32 CPU cores. By default the ESXi hosts that are simulated have 8 cores. I did a bit of digging around in the /etc/vmware-vpx/vcsim/model folder and figured out which files were referenced when launching the simulator with the default option. By default, the host model in the ESX50 folder is used, so naturally, in order to configure custom ESXi hosts, we need to edit the files within this folder.

Initially, I found one file, “HostHardwareInfo.xml” and changed the CPU core count value to 32. This appeared to work – starting up the sim, and looking at the Web Client, I saw that the simulated hosts were now showing 32 CPU cores. I also changed the RAM up to 32GB (from the default of 16) just to test another option, and this was also showing up. However, upon loading up the MOB (Managed Object Browser), and navigating to the these hosts, I saw that the properties under the host summary->config->hardware were telling another story – they were still set to 8 cores and 16GB RAM. A little more digging revealed that another file, “HostListSummary.xml” also needed to be updated.

So in order to setup your custom ESXi host models for the default VCSIM profile, make sure you update both of these files.

The files to update your default ESXi model
The files to update your default ESXi model


Here is the small change I made to increase the Host core count to 32 cores.


And the data reflected in the MOB:

ESXi Host Hardware Summary


Changes as seen in the vSphere Web Client:

vSphere Web Client Host Hardware Summary

Make sure you backup these files before changing them, so that you can roll back if you need to. There are other ways of creating your own profiles for the simulator, but I could not find any documentation on how to create custom hosts. The only bits I could find were relating to creating your own datastores. You can also use the default profile template to create your own profile in it’s entirety, and this is a better long term solution, however to get things up and running quickly with the default profile, the above works nicely.

Note that all properties and methods pertaining to each managed object found in the API appear to be set up and created when using the VCSIM, so this makes a great development/testing/lab tool. Kudos to VMware for releasing this with the VCSA, and thanks to William Lam for pointing it out and blogging about it!