Summary: Info and tips about VM Affinity rules on VMware, as well as scripts on how to export and import them.
Date: Around 2014
Refactor: 1 May 2025: Checked links and formatting.

If a service request regarding VM affinity is received you should follow this procedure to implement the service request:

1. Check validity of service request
2. Create groups if required
3. Create affinity rule
4. Update documentation

VMs can only have a (anti-)affinity if they are part of the same cluster. So always check first if the VMs are in the same cluster. If not, deny the request, if they are, continue.

If the request if to host a VM onto specific hosts you first need to create groups, even if it's just one VM of just one host. VM-Host rules only work with groups.

To create a group follow these steps:

• Right-click the specific cluster and select “Edit Settings”
• Go to “VMware DRS” → DRS Groups Manager
• Click Add on the Virtual Machines DRS groups of Host DRS Group section
• Enter a name and select the VMs/Hosts that should be in the group
• Click OK to create the group

To create the actual affinity rule follow these steps:

• Right-click the specific cluster and select “Edit Settings”
• Go to “VMware DRS” → Rules
• Click Add
• Enter a name and select the type:
  • Keep Virtual Machines together
  • Separate Virtual Machines
  • Virtual Machines to Hosts
• Select the required VMs, or if selected the Virtual Machines to Hosts option the required VM and Hosts group you just created.
• Note that in the last case you also have these options:
  • Must run on hosts in group
  • Should run on hosts in group
  • Must not run on hosts in group
  • Should not run on hosts in group
  • Save the rule by clicking OK

Because DRS rules can get lost when DRS gets disabled you should document the rules very precise. Luckily there are export and import scrips:

$outfile = "C:\rules.txt"
Remove-Item $outfile
$clusterName = <cluster-name>
$rules = get-cluster -Name $clusterName | Get-DrsRule
 
foreach($rule in $rules){
  $line = (Get-View -Id $rule.ClusterId).Name
  $line += ("," + $rule.Name + "," + $rule.Enabled + "," + $rule.KeepTogether)
  foreach($vmId in $rule.VMIds){
    $line += ("," + (Get-View -Id $vmId).Name)
  }
  $line | Out-File -Append $outfile
}

$file = "C:\rules.txt"
$rules = Get-Content $file
 
foreach($rule in $rules){
  $ruleArr = $rule.Split(",")
  if($ruleArr[2] -eq "True"){$rEnabled = $true} else {$rEnabled = $false}
  if($ruleArr[3] -eq "True"){$rTogether = $true} else {$rTogether = $false}
  get-cluster $ruleArr[0] | `
    New-DrsRule -Name $ruleArr[1] -Enabled $rEnabled -KeepTogether $rTogether -VM (Get-VM -Name ($ruleArr[4..($ruleArr.Count - 1)]))
}

The scripts are originally created by LucD