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Document DRS Rules with PowerCLI

As a consultant, I find myself doing a lot of reconnaissance within customers’ vSphere environments.  Here’s how to document DRS Rules with PowerCLI.

DRS Rules – Why have them?

You can use DRS rules for numerous purposes.  Use them to provide better reliability for applications and services.   You can also use them to ensure licensing compliance, and for other pragmatic purposes.

Here’s a very quick set of hand rules for DRS rules:

  • Use VM anti-affinity DRS rules to ensure redundant VMs are not running on the same host within a cluster.  In these configurations, having only one of the VMs up keeps the service or application online.  Examples include cluster members, web farm members, domain controllers, DNS servers, etc.  (Note: for Microsoft clusters, don’t forget to include File Share Witnesses in the rule as well as the nodes!)
  • Use VM affinity DRS rules for VMs that in total comprise a service and/or application.  In these configurations, downtime for any single VM in the group causes the entire application or service to be inoperable.  Examples include a web front end server, an application middleware server, and database backend server.  Or perhaps an email fax server that depends upon an email server.
  • Use VM host affinity/anti-affinity should DRS rules to try to ensure a VM runs or doesn’t run on specific hosts, but it can violate the rule if required, such as possible preferred nodes are down.  An example would be for vCenter to run on a specific host in case the vCenter VM goes down.  You then likely know which host to log directly into to start it back up.  Otherwise, if that preferred node is down, the VM can run on another node.
  • Use VM to host affinity must DRS rules to ensure a VM will only run on specific VMs, even if that results in downtime if those hosts aren’t up.  Must rules generally should only be used for licensing compliance purposes, where the software vendor licenses the product on all possible potential physical nodes it can run on, not how many hosts it could be actively running on at any given point in time.

Document DRS Rules with PowerCLI – Rules

DRS rules are a little bit of a challenge.  Members are a multi-valued property with VM IDs, which isn’t particularly useful.  We need to work a little magic to translate VM IDs to VM names, and then join the multi-valued property to allow it to be exportable into CSVs, etc.

This can be accomplished using the Get-DrsRule cmdlet.

Get-DrsRule -Cluster ClusterName | Select Name, Enabled, Type, @{Name="VM"; Expression={ $iTemp = @(); $_.VMIds | % { $iTemp += (Get-VM -Id $_).Name }; [string]::Join(";", $iTemp) }}

Now you can tack on an export-csv or what not to it, and it’s readable with useful information us humans would understand.

Note, there is also a specific cmdlet to get DRS to host rules only if that’s what you’re looking for : Get-DrsVMHostRule, but the above gets all DRS rules.

Document DRS Rules with PowerCLI – Groups

DRS rules can also have groups, so it’s important that they’re documented as well.  Members are a multi-valued property, but that’s the only challenge here.  We just need to use a join method to make it readable.

This can be accomplished using the Get-DrsClusterGroup cmdlet.

Get-DrsClusterGroup -Cluster ClusterName | select Name, Cluster, GroupType, @{Name="Member:"; Expression={[string]::Join(";", $_.Member)}}

Now you can tack on an export-csv or what not to it.