Tenant workloads run on the ESXi hosts in the shared edge and compute cluster. Due to the shared nature of the cluster, NSX Controllers and Edge devices run in this cluster. The design decisions determine the number of hosts and vSphere HA settings and several other characteristics of the shared edge and compute cluster.

Table 1. Shared Edge and Compute Cluster Design Decisions

Decision ID

Design Decision

Design Justification

Design Implication

SDDC-VI-VC-017

Create a shared edge and compute cluster for the NSX Controllers and NSX Edge gateway devices.

NSX Manager requires a 1:1 relationship with a vCenter Server system.

Each time you provision a Compute vCenter Server system, a new NSX Manager is required.

Set anti-affinity rules to keep each Controller on a separate host. A 4-node cluster allows maintenance while ensuring that the 3 Controllers remain on separate hosts.

SDDC-VI-VC-018

Configure Admission Control for 1 host failure and percentage based failover capacity.

vSphere HA protects the NSX Controller instances and edge services gateway devices in the event of a host failure. vSphere HA powers on virtual machines from the failed hosts on any remaining hosts.

Only a single host failure is tolerated before potential resource contention.

SDDC-VI-VC-019

Create shared edge and compute cluster with a minimum of 4 hosts.

  • 3 NSX Controllers are required for sufficient redundancy and majority decisions.

  • One host is available for failover and to allow for scheduled maintenance.

4 hosts is the smallest starting point for the shared edge and compute cluster for redundancy and performance thus increasing cost over a 3 node cluster.

SDDC-VI-VC-020

Set up VLAN-backed port groups for external access and management on the shared edge and compute cluster hosts.

Edge gateways need access to the external network in addition to the management network.

VLAN-backed port groups must be configured with the correct number of ports, or with elastic port allocation.

SDDC-VI-VC-021

Create a resource pool for the required SDDC NSX Controllers and edge appliances with a CPU share level of High, a memory share of normal, and 16 GB memory reservation.

The NSX components control all network traffic in and out of the SDDC as well as update route information for inter-SDDC communication. In a contention situation it is imperative that these virtual machines receive all the resources required.

During contention SDDC NSX components receive more resources then all other workloads as such monitoring and capacity management must be a proactive activity.

SDDC-VI-VC-022

Create a resource pool for all user NSX Edge devices with a CPU share value of Normal and a memory share value of Normal.

NSX edges for users, created by vRealize Automation, support functions such as load balancing for user workloads. These edge devices do not support the entire SDDC as such they receive a lower amount of resources during contention.

During contention these NSX edges will receive fewer resources than the SDDC edge devices. As a result, monitoring and capacity management must be a proactive activity.

SDDC-VI-VC-023

Create a resource pool for all user virtual machines with a CPU share value of Normal and a memory share value of Normal.

Creating virtual machines outside of a resource pool will have a negative impact on all other virtual machines during contention. In a shared edge and compute cluster the SDDC edge devices must be guaranteed resources above all other workloads as to not impact network connectivity. Setting the share values to normal gives the SDDC edges more shares of resources during contention ensuring network traffic is not impacted.

During contention user workload virtual machines could be starved for resources and experience poor performance. It is critical that monitoring and capacity management must be a proactive activity and that capacity is added or a dedicated edge cluster is created before contention occurs.

The following table summarizes the attributes of the shared edge and compute cluster logical design. The number of VMs on the shared edge and compute cluster will start low but will grow quickly as user workloads are created.

Table 2. Shared Edge and Compute Cluster Logical Design Background

Attribute

Specification

Minimum number of hosts required to support the shared edge and compute cluster

4

Capacity for host failures per cluster

1

Number of usable hosts per cluster

3