Using soft constraints to select a specific Cloud Zone based upon performance tier

Products

• VMware Aria Suite

Issue/Introduction

• You have two or more Cloud Zones systems are being provisioned to.
• Each Cloud Zone is uniquely tagged with High, Medium, and Standard (or some variation of this combination)
• All Cloud Zones have a priority affinity of 0.
• When targeting the lower-tier performance Cloud Zone using a soft constraint, the request is instead placed on a higher performance tier.

Environment

VMware Aria Automation 8.x

Cause

 

• Soft constraints allow the system to express a preference, which is honored only if the resources are available. However, soft constraints may not be applied if there are conflicting project placement policies or if all zones have identical Priority Affinity values.
• Specifically, using a project placement policy set to "SPREAD" will distribute workloads across all available zones, potentially overriding the intended behavior of soft constraints.

 

Resolution

To address this issue, there are two possible approaches:

1. Modify Cloud Zone Affinity with "SPREAD" Placement Policy:

   • If continuing to use the "SPREAD" policy, adjust the Priority Affinity settings of Cloud Zones:
     • For instance, set the following Priority Affinity:
       • High: 1
       • Standard: 0
     • If more tiers exist:
       • High: 2
       • Medium: 1
       • Standard: 0
   • These affinity settings will ensure that when a soft constraint is used, the preferred Cloud Zone is selected as intended, even while maintaining workload distribution with "SPREAD."

2. Change to the "DEFAULT" Project Placement Policy:

   • Switch the project placement policy to "DEFAULT".
   • This approach respects soft constraints more directly, especially when Cloud Zones are set with the same Priority Affinity (0). This ensures that deployments prioritize the intended zone as indicated by the soft constraints without requiring changes to affinity values.

Additional Considerations:

• Advanced Placement Mechanism:

  • Note that advanced placement settings are also part of the Cloud Zone mechanism but relate to specific host-level optimizations (e.g., VMware vRealize Operations). Advanced placement should not impact the basic project-level placement unless specific configurations overlap.

• Project Placement Policy Details:

  • The placement policy configured for a project determines the ordering of Cloud Zones during placement selection:
    • SPREAD: Prioritizes even distribution, which may override soft constraints.
    • DEFAULT: Orders Cloud Zones according to soft constraints when set with equal affinity values.

Additional Information

Using constraint tags in Automation Assembler