VMware Cloud Foundation distributes the functionality of the SDDC across multiple workload domains and vSphere clusters. A workload domain, whether it is the management workload domain or a VI workload domain, is a logical abstraction of compute, storage, and network capacity, and consists of one or more vSphere clusters. Each cluster can exist vertically in a single rack or be spanned horizontally across multiple racks.

The relationship between workload domain clusters and data center racks in VMware Cloud Foundation is not one-to-one. While a workload domain cluster is an atomic unit of repeatable building blocks, a rack is a unit of size. Because workload domain clusters can have different sizes, you map workload domain clusters to data center racks according to your requirements and physical infrastructure constraints. You determine the total number of racks for each cluster type according to your scalability needs.

Table 1. Workload Domain Cluster to Rack Configuration Options

Workload Domain Cluster to Rack Configuration

Description

Workload domain cluster in a single rack

  • The workload domain cluster occupies a single rack.

  • Can be used for shared edge and compute workloads in the same cluster.

  • Can be dedicated for compute-only workloads or for NSX Edge-only clusters.

Workload domain cluster spanning multiple racks

  • The management domain default cluster can span multiple racks if the data center fabric can provide Layer 2 adjacency, such as VXLAN overlay in the fabric, between racks. If the Layer 3 fabric does not support this requirement, then the management default cluster must be mapped to a single rack.

  • A VI workload domain cluster dedicated to compute-only workloads, without SDDC Manager deployed NSX Edge clusters, can span racks when using NSX Overlay in conjuction with a Layer 3 network fabric without Layer 2 adjacency between racks.

  • A vSphere cluster that is to host only an NSX Edge cluster, deployed from SDDC Manager, must be deployed in a single rack. To increase redundancy, you must deploy two vSphere clusters to two separate racks with edge nodes in both racks.

Workload domain cluster with multiple availability zones, each zone in a single rack

  • To span multiple availability zones, the network fabric must support stretched Layer 2 networks and Layer 3 routed networks between the availability zones.

  • A cluster spanning multiple racks is not supported with multiple availability zones.
Figure 1. Workload Domain Cluster in a Single Rack

One rack runs the cluster(s) from each workload domain.
Figure 2. Workload Domain Cluster Spanning Multiple Racks

The hosts in the compute only workload domain cluster horizontally span racks. The management cluster and vSphere clusters for NSX edges are deployed vertically in a single rack.
Figure 3. Workload Domain Cluster with Multiple Availability Zones, Each Zone in One Rack

Two availability zones of infrastructure, the workload domain cluster hosts in each zone are in one rack.