The functionality in an SDDC is distributed across multiple workload domains and vSphere clusters. A workload domain, whether it is a management domain or virtual infrastructure workload domain, is a logical abstraction of compute, storage, and network cloud capacity and consists of one or more clusters. Each cluster can exist vertically in a single rack or be spanned horizontally across multiple racks. You determine the total number of racks for each cluster type according to your scalability needs.
When using a Layer 3 network fabric, the clusters in the management domain cannot span racks. Management appliances and virtual machines rely on VLAN-backed networks. The physical network configuration terminates Layer 2 networks in each rack at the top-of-rack (ToR) switch. Therefore, you cannot migrate a virtual machine to a different rack because the IP subnet is available only in the rack where the virtual machine is currently running. However, you can map each management cluster to a single rack.
Management Domain to Rack Configuration |
Description |
|---|---|
Management domain in one rack |
The management domain can occupy exactly one rack, whether it consists of a single or multiple clusters. |
Management domain across multiple racks |
To span multiple racks, the network fabric must support stretched Layer 2 networks between these racks. Otherwise, map each cluster in the management domain to a single rack. |
| Management domain with multiple availability zones, each zone in one rack | To span multiple availability zones, the network fabric must support stretched Layer 2 networks between the availability zones. |
| Management domain with multiple availability zones, each zone spanning multiple racks | To span multiple availability zones, the network fabric must support stretched Layer 2 networks between the availability zones. Otherwise, map each cluster in the management domain to a single rack. |
In an environment with multiple VMware Cloud Foundation instances, for example, you can have two availability zones in the first instance only. Each zone spans over the default management cluster on a single rack server.