Before you can stretch a cluster, you must meet the prerequisites.

  • Open the Deployment of Multiple Availability Zones document and read it to understand the requirements.
  • Ensure a vSAN Enterprise license has been applied to the cluster to be stretched. A vSAN Enterprise license is required for stretching a cluster. See KB 70328 for information about a known licensing issue.
  • The management VLAN between the two availability zones must be stretched.
  • All VMs on an external network must be on a virtual wire. If they are on a VLAN, that VLAN must be stretched as well.
  • Each availability zone must have its own vMotion, vSAN, and VXLAN networks.
  • The vMotion, vSAN, and VXLAN networks require L3 routing between the availability zones. vSAN networks must also have L3 routing to the vSAN network of the witness host.
  • The VLAN IDs must be identical on both availability zones.
  • Each stretched cluster requires a vSAN witness appliance in a third party location. The witness appliance should be running the same version of ESXi as the ESXi hosts in the stretched cluster. The maximum RTT on the witness is 200ms. Follow the steps described in Deploy the vSAN Witness Host in Region B to add and configure a vSAN witness.
  • If you are stretching a cluster in a VI workload domain, you must stretch the management domain cluster first. vCenter Servers for all workload domains are in the management domain. Hence, you must protect the management domain to ensure that you can access and manage the workload domains.
  • Ensure that you have enough hosts such that there is an equal number of hosts on each availability zone. This is to ensure that there are sufficient resources in case an availability zone goes down completely.
  • TCP port and UDP Ports needs to be open for witness traffic between the witness host and the vSAN cluster data nodes. See KB article 52959.

VMware Cloud Foundation Networks

Network Name Connectivity to AZ2 Minimum MTU Maximum MTU
vSAN L3 1500 9000
vMotion L3 1500 9000
VXLAN (VTEP) L3 1600 9000
Management L2 1500 9000
Witness Management L3 1500 9000
Witness vSAN L3 1500 9000