How to use affinity and anti‑affinity rules
Affinity and anti-affinity rules determine whether or not VMs are kept together as they are moved around within your environment.
Affinity rules keep VMs together on the same host
Anti-affinity rules ensure that VMs are distributed across different hosts
For example, if it's important that your application has very low latency, you can create affinity rules to make sure that the application's VMs are always kept on the same host. If you want your application to be robust in the event of host failures, you can create anti-affinity rules to spread the VMs across multiple hosts.
Excessive use of affinity and anti-affinity rules can cause unpredictable VM and platform performance issues. For example, VMs involved in rules may have an increased likelihood of migrating between hosts simultaneously. Adding a large number of VMs to an affinity rule may cause performance issues if all of the VMs become busy simultaneously. An anti-affinity rule with a large number of VMs may not be honoured if the platform is unable to place the VMs on separate hosts.
UKCloud reserves the right to disable or disregard rules if required for maintenance or platform management.
To complete the steps in this guide you must have access to the UKCloud Portal and VMware Cloud Director.
Creating an affinity or anti-affinity rule
To create an affinity or anti-affinity rule:
In the VMware Cloud Director Virtual Data Center dashboard, select the VDC in which you want to create the affinity or anti-affinity rule.
In the left navigation panel, under Compute, select Affinity Rules.
To create an affinity rule, in the Affinity Rules section, click New.
To create an anti-affinity rule,in the Anti-Affinity Rules section, click New.
In the Create Affinity Rule or Create Anti-Affinity Rule dialog box, enter a Name for the rule.
If you don't want the rule to take effect immediately, deselect the Enabled check box.
If you leave this check box selected, the rule is applied and the selected VMs are redistributed as required as soon as you create the rule.
If you leave the Required check box selected, the VMs added to the rule will not power on if the rule cannot be met. If you want the VMS to be powered on even if the rule cannot be met, deselect the Required check box to create the rule as a preferred rule instead.
In the VMs in Rule section, select the VMs that you want to add to the rule.
Select the Show selected option to see a list of the VMs already included in the rule.
When you're done, click Save.
For more information about UKCloud for VMware see the Getting Started Guide for UKCloud for VMware.
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