Create server and site affinity rules for VMs

Applies to: Azure Stack HCI, version 22H2

Using either Windows Admin Center or Windows PowerShell, you can easily create affinity and anti-affinity rules for your virtual machines (VMs) in a cluster.

Affinity is a rule that establishes a relationship between two or more resource groups or roles, such as VMs, to keep them together on the same server, cluster, or site. Anti-affinity is the opposite in that it's used to keep the specified VMs or resource groups apart from each other, such as two domain controllers placed on separate servers or in separate sites for disaster recovery.

Affinity and anti-affinity rules are used similarly to the way Azure uses Availability Zones. In Azure, you can configure Availability Zones to keep VMs in separate zones and away from each other or in the same zone with each other.

Using affinity and anti-affinity rules, any clustered VM would either stay in the same cluster node or be prevented from being together in the same cluster node. In this way, the only way to move a VM out of a node would be to do it manually. You can also keep VMs together with its own storage, such as the Cluster Shared Volume (CSV) that its VHDX resides on.

Using Windows Admin Center

You can create basic affinity and anti-affinity rules using Windows Admin Center.

1. In Windows Admin Center home, under All connections, select the server or cluster you want to create the VM rule for.
2. Under Tools, select Settings.
3. Under Settings, select Affinity rules, then select Create rule under Affinity rules.
4. Under Rule name, enter a name for your rule.
5. Under Rule type, select either Together (same server) or Apart (different servers) to place your VMs on the same server or on different servers.
6. Under Applies to, select the VMs that this rule applies to. Use the Add button to add more VMs to the rule.
7. When finished, select Create rule.
8. To delete a rule, select it and select Delete rule.

Using Windows PowerShell

You can create more complex rules using Windows PowerShell than using Windows Admin Center. Typically, you set up your rules from a remote computer, rather than on a host server in a cluster. This remote computer is called the management computer.

When running Windows PowerShell commands from a management computer, include the -Name or -Cluster parameter with the name of the cluster you're managing. If applicable, you also need to specify the fully qualified domain name (FQDN) when using the -ComputerName parameter for a server node

New PowerShell cmdlets

To create affinity rules for clusters, use the following new PowerShell cmdlets:

New-ClusterAffinityRule

The New-ClusterAffinityRule cmdlet is used to create new rules. With this command you would specify the name of the rule and the type of rule it is, where:

-Name is the name of the rule

-RuleType values are SameFaultDomain | SameNode | DifferentFaultDomain | DifferentNode

Example:

New-ClusterAffinityRule -Name Rule1 -RuleType SameFaultDomain

Set-ClusterAffinityRule

The Set-ClusterAffinityRule cmdlet is used to enable or disable a rule, where:

-Name is the name of the rule to enable or disable

-Enabled | Disabled enables or disables the rule

Example:

Set-ClusterAffinityRule -Name Rule1 -Enabled

Get-ClusterAffinityRule

The Get-ClusterAffinityRule cmdlet is used to display the specified rule and what type it is. If -Name isn't specified, it lists all rules.

Example:

Get-ClusterAffinityRule -Name Rule1

Add-ClusterGroupToAffinityRule

The Add-ClusterGroupToAffinityRule cmdlet is used to add a VM role or group name to a specific affinity rule, where:

-Groups is the name of the group or role to add to the rule.

-Name is the name of the rule to add to.

Example:

Add-ClusterGroupToAffinityRule -Groups Group1 -Name Rule1

Add-ClusterSharedVolumeToAffinityRule

The Add-ClusterSharedVolumeToAffinityRule allows your VMs to stay together with the Cluster Shared Volume the VHDX resides on, where:

-ClusterSharedVolumes is the CSV disk that you wish to add to the rule

-Name is the name of rule to add to

Example:

Add-ClusterSharedVolumeToAffinityRule -ClusterSharedVolumes CSV1 -Name Rule1

Remove-ClusterAffinityRule

The Remove-ClusterAffinityRule deletes the specified rule, where -Name is the name of the rule.

Example:

Remove-ClusterAffinityRule -Name Rule1

Remove-ClusterGroupFromAffinityRule

The Remove-ClusterGroupFromAffinityRule removes a VM group or role from a specific rule but doesn't disable or delete the rule, where:

-Name is the name of the rule

-Groups are the groups or roles that you wish to remove from the rule

Example:

Remove-ClusterGroupFromAffinityRule -Name Rule1 -Groups Group1

Remove-ClusterSharedVolumeFromAffinityRule

The Remove-ClusterSharedVolumeFromAffinityRule cmdlet is used to remove the Cluster Shared Volumes from a specific rule but doesn't disable or delete the rule, where:

-ClusterSharedVolumes is the CSV disk that you want to remove from the rule.

-Name is the name of the rule to add to.

Example:

Remove-ClusterSharedVolumeFromAffinityRule -ClusterSharedVolumes CSV1 -Name Rule1

Existing PowerShell cmdlets

With the advent of the new cmdlets, we also added extra new switches to a few existing cmdlets.

Move-ClusterGroup

The new -IgnoreAffinityRule switch ignores the rule and moves the cluster resource group to another cluster node. For more information on this cmdlet, see Move-ClusterGroup.

Example:

Move-ClusterGroup -IgnoreAffinityRule -Cluster Cluster1

Start-ClusterGroup

The new -IgnoreAffinityRule switch ignores the rule and brings the cluster resource group online in its current location. For more information on this cmdlet, see Start-ClusterGroup.

Example:

Start-ClusterGroup -IgnoreAffinityRule -Cluster Cluster1

Affinity rule examples

Affinity rules are "together" rules that keep resources on the same server, cluster, or site. Here are a few common scenarios for setting up affinity rules.

Scenario 1

Suppose you have a SQL Server VM and a Web Server VM. These two VMs need to always remain in the same site but don't necessarily need to be on the same cluster node in the site. Using SameFaultDomain, this is possible, as shown:

New-ClusterAffinityRule -Name WebData -Ruletype SameFaultDomain -Cluster Cluster1

Add-ClusterGroupToAffinityRule -Groups SQL1,WEB1 -Name WebData -Cluster Cluster1

Set-ClusterAffinityRule -Name WebData -Enabled 1 -Cluster Cluster1

To see this rule and how it's configured, use the Get-ClusterAffinityRule cmdlet to see the output:

Get-ClusterAffinityRule -Name WebData -Cluster Cluster1

Name        RuleType          Groups        Enabled
----        ---------         ------        -------
WebData     SameFaultDomain   {SQL1, WEB1}     1

Scenario 2

Let's use the same scenario except specify that the VMs must reside on the same cluster node. Using SameNode, set it as follows:

New-ClusterAffinityRule -Name WebData1 -Ruletype SameNode -Cluster Cluster1

Add-ClusterGroupToAffinityRule -Groups SQL1,WEB1 -Name WebData1 -Cluster Cluster1

Set-ClusterAffinityRule -Name WebData1 -Enabled 1 -Cluster Cluster1

To see the rule and how it's configured, use the Get-ClusterAffinityRule cmdlet to see the output:

Get-ClusterAffinityRule -Name WebData1 -Cluster Cluster1

Name    RuleType    Groups        Enabled
----    --------    ------        -------
DC      SameNode    {SQL1, WEB1}     1

Anti-affinity rule examples

Anti-affinity rules are "apart" rules that separate resources and place them on different servers, clusters, or sites.

Scenario 1

You have two VMs each running SQL Server on the same Azure Stack HCI multi-site cluster. Each VM utilizes a lot of memory, CPU, and storage resources. If the two end up on the same node, this can cause performance issues with one or both as they compete for memory, CPU, and storage cycles. Using an anti-affinity rule with DifferentNode as the rule type, these VMs will always stay on different cluster nodes.

The example commands would be:

New-ClusterAffinityRule -Name SQL -Ruletype DifferentNode -Cluster Cluster1

Add-ClusterGroupToAffinityRule -Groups SQL1,SQL2 –Name SQL -Cluster Cluster1

Set-ClusterAffinityRule -Name SQL -Enabled 1 -Cluster Cluster1

To see the rule and how it's configured, use the Get-ClusterAffinityRule cmdlet to see the output:

Get-ClusterAffinityRule -Name SQL -Cluster Cluster1

Name    RuleType        Groups        Enabled
----    -----------     -------       -------
SQL     DifferentNode   {SQL1, SQL2}     1

Storage affinity rules

You can also keep a VM and its VHDX on a Cluster Shared Volume (CSV) on the same cluster node. Doing so would keep CSV redirection from occurring, which can slow down the starting or stopping of a VM. Taking into account the combined affinity and anti-affinity scenario previously, you can keep the SQL VM and the Cluster Shared Volume on the same cluster node. To do that, use the following commands:

New-ClusterAffinityRule -Name SQL1CSV1 -Ruletype SameNode -Cluster Cluster1

New-ClusterAffinityRule -Name SQL2CSV2 -Ruletype SameNode -Cluster Cluster1

Add-ClusterGroupToAffinityRule -Groups SQL1 -Name SQL1CSV1 -Cluster Cluster1

Add-ClusterGroupToAffinityRule -Groups SQL2 -Name SQL2CSV2 -Cluster Cluster1

Add-ClusterSharedVolumeToAffinityRule -ClusterSharedVolumes CSV1 -Name SQL1CSV1 -Cluster Cluster1

Add-ClusterSharedVolumeToAffinityRule -ClusterSharedVolumes CSV2 -Name SQL2CSV2 -Cluster Cluster1

Set-ClusterAffinityRule -Name SQL1CSV1 -Enabled 1 -Cluster Cluster1

Set-ClusterAffinityRule -Name SQL2CSV2 -Enabled 1 -Cluster Cluster1

To see these rules and how they're configured, use the Get-ClusterAffinityRule cmdlet without the -Name switch and view the output.

Get-ClusterAffinityRule -Cluster Cluster1

Name        RuleType               Groups            Enabled
----        --------               ------            -------
Site1Trio   SameFaultDomain        {SQL1, WEB1, DC1}    1
Site2Trio   SameFaultDomain        {SQL2, WEB2, DC2}    1
TrioApart   DifferentFaultDomain   {DC1, DC2}           1
SQL1CSV1    SameNode               {SQL1, <CSV1-GUID>}  1
SQL2CSV2    SameNode               {SQL2, <CSV2-GUID>}  1

Next steps

Learn how to manage your VMs. See Manage VMs on Azure Stack HCI using Windows Admin Center.