I was in a meeting last week with Engineering and a question had come up on whether customers were actively using the Anti-Affinity (AA) VM-Host Rules capability and if so, what are some of the use cases? We know that Anti-Affinity VM-VM Rules are used quite regularly by customers and the use cases are pretty well understood, but what is not clear was the usage and frequency of AA VM-Host rules. I figured I could help Engineering by asking some of my Twitter folllowers, the following question:

Anyone using Anti-Affiity VM-Host Rules today (e.g. VMs should/must not run on specific ESXi hosts)? Had a chat w/Engr the other day, they were curious if customers used this at all compared to Affinity VM-Host Rules & what the use case might be? pic.twitter.com/7EASBAvvt5 — William Lam (@lamw) June 21, 2018

In an attempt to avoid any confusion, I also included a screenshot of the AA VM-Host Rules in the vSphere UI which you can see above. However, it looks like my attempt had failed and I actually received a number of replies that described AA VM-VM Host Rules (separate certain groups of VMs from each other, regardless of host groups), rather than AA VM-Host Rules (do not run certain groups of VMs on specific host groups). Perhaps the question could have been better phrased or it was just a simple misinterpretation, but overall it was a very useful exercise and it was great learn about all the different use cases for BOTH AA VM-VM and AA VM-Host Rules, so thank you to everyone who shared their feedback.

Just like Engineering, I am sure others would like to know how AA VM-Host Rules are used by other, so I have aggregated all use cases related to AA VM-Host Rules into a single Twitter Moment (never knew what this was until last week) which folks can access by visiting: Anti-Affinity VM-Host Rules Usage

Here are the common use cases from looking at the feedback:

Licensing

Non-uniform hardware capabilities (CPU core/sockets, GPUs, etc)

Stretched/Metro Clustering

Inconsistency of software configuration generally related to networking or storage

There were actually a few folks who had great point that you can use AA VM-Host rules to easily describe an Affinity VM-Host scenario. Take this example by Darryl Irvine:

This. 👍 Easier to say don’t run on 2 hosts rather than must run on 20. — Darryl Irvine (@worm_za) June 21, 2018

Again, I want to thank everyone who participated and shared their perspectives, this was not only helpful to Engineer but I think it also helped others (received a number of private messages saying that this helped validate their use or that folks learned about new methods on solving the exact same set of problems). I am sure there are more valid use cases, feel free to leave a comment or better yet, reply back to the original tweet and I can include it in the Twitter Moment for others to benefit from.