The management cluster design determines the number of hosts and vSphere HA settings for the management cluster.

Table 1. Design Decisions on the Management Cluster

Decision ID

Design Decision

Design Justification

Design Implication

SDDC-VI-VC-014

In Region A, create a management cluster with a minimum of 4 ESXi hosts for a single availability zone or with a minimum of 8 ESXi hosts for two availability zones (minimum of 4 ESXi hosts in each availability zone).

Allocating four ESXi hosts provides full redundancy for each availability zone within the cluster.

Having four ESXi hosts in each availability zone guarantees vSAN and NSX redundancy during availability zone outages or maintenance operations.

Additional ESXi host resources are required for redundancy.

SDDC-VI-VC-015

In Region B, create a management cluster with 4 ESXi hosts.

Allocating four ESXi hosts provides full redundancy for the cluster. Having four ESXi hosts guarantees vSAN and NSX redundancy during maintenance operations.

Additional ESXi host resources are required for redundancy.

SDDC-VI-VC-016

When using a single availability zone, configure Admission Control for 1 ESXi host failure and percentage-based failover capacity.

Using the percentage-based reservation works well in situations where virtual machines have varying and sometime significant CPU or memory reservations.

vSphere 6.5 automatically calculates the reserved percentage based on ESXi host failures to tolerate and the number of ESXi hosts in the cluster.

In a four ESXi host management cluster, only the resources of three ESXi hosts are available for use.

SDDC-VI-VC-017

When using two availability zones, configure Admission Control for percentage-based failover based on half of the ESXi hosts in the cluster.

Allocating only half of a stretched cluster ensures that all VMs have enough resources if an availability zone outage occurs.

In an eight-host management cluster, only the resources of four ESXi hosts are available for use.

If you add more ESXi hosts to the management cluster, add them in pairs, one in each availability zone.

SDDC-VI-VC-018

When using two availability zones, set the cluster isolation addresses for the cluster to the gateway IP address for the vSAN network in both availability zones.

Allows vSphere HA to validate complete network isolation in the case of a connection failure between availability zones.

You must manually configure the isolation address.

SDDC-VI-VC-019

When using two availability zones, set the advanced cluster setting das.usedefaultisolationaddress to false.

Ensures that the manual isolation addresses are used instead of the default management network gateway address.

None.

SDDC-VI-VC-020

When using a single availability zone, create a host profile for the management cluster.

Using host profiles simplifies configuration of ESXi hosts and ensures that the settings are uniform across the cluster.

Anytime an authorized change to an ESXi host is made, the host profile must be updated to reflect the change or the status will show non-compliant.

SDDC-VI-VC-021

When using two availability zones, create a host profile for each availability zone in the management cluster.

Using host profiles simplifies configuration of ESXi hosts and ensures that the settings are uniform across the availability zones in the cluster.

Anytime an authorized change to an ESXi host is made, the host profile must be updated to reflect the change or the status will show non-compliant.

Because of configuration differences between availability zones, two host profiles are required and must be applied on each ESXi host.

The management cluster logical design has the following attributes:

Table 2. Management Cluster Logical Design Background

Attribute

Specification

Number of ESXi hosts required to support management hosts with no over commitment

2

Number of ESXi hosts recommended because of operational constraints (ability to take a host offline without sacrificing high availability capabilities)

4

Number of ESXi hosts recommended because of operational constraints, while using vSAN (ability to take a host offline without sacrificing high availability capabilities) .

  • 4 (single availability zone)

  • 8 (two availability zones)

Capacity for ESXi host failures per cluster

  • 25% reserved CPU RAM (single availability zone)

  • 50% reserved CPU RAM (two availability zones)