You can expand a stretched cluster by adding hosts. The hosts need to be added in pairs (such as two, four, six, or eight). Half of the hosts you add to the cluster will be added to the first availability zone and the other half will be added to the second availability zone.

Prerequisites

You must have a stretched cluster and available hosts.

Procedure

  1. Commission the additional hosts to VMware Cloud Foundation. For each pair of hosts, associate one with the network pool in AZ1 and the other with the network pool in AZ2.
    See Commission Hosts.
  2. SSH in to the SDDC Manager appliance using the vcf administrative user account.
  3. Enter su to switch to the root user and navigate to the /opt/vmware/sddc-support directory.
  4. Enter the following command: 
    ./sos --expand-stretch-cluster --sc-domain <DOMAIN NAME> --sc-cluster <CLUSTER NAME> --sc-hosts <HOSTFQDN,HOSTDQND2,...> --esxi-license-key <LICENSE KEY>
    Example input and response: 
    root@sddc-manager [ /opt/vmware/sddc-support ]# ./sos --expand-stretch-cluster --sc-domain MGMT --sc-cluster SDDC-Cluster1 --sc-hosts esxi-9.vrack.vsphere.local, esxi-10.vrack.vsphere.local --esxi-license-key AAAAA-BBBBB-CCCCC-DDDDD-EEEEE
Welcome to Supportability and Serviceability(SoS) utility!
Logs : /var/log/vmware/vcf/sddc-support/stretchCluster-2019-02-20-10-04-32-123007
Stretch Cluster operation log : /var/log/vmware/vcf/sddc-support/stretchCluster-2019-02-20-10-04-32-123007/sos.log
Starting vSAN stretched cluster operations..
expand vSAN stretched cluster operation started
Api Response:{
  "taskId": "6e4b13d9-eead-408b-a595-4e89ef885a3e",
  "resourceId": "0c518498-b302-40ae-abc4-10addead7bc2",
  "resourceType": "ESXI",
  "state": "IN_PROGRESS",
  "description": "Prepare vSAN Cluster - SDDC-Cluster1 for Stretch in VMware Cloud Foundation",
  "timestamp": 1550657073615,
  "id": "6e4b13d9-eead-408b-a595-4e89ef885a3e"
}
  5. Monitor the state of the task in the SDDC Manager Dashboard.
  6. If required, SSH in to each newly added hosts and add a static route to the vSAN network of the witness host. Add static routes in the witness if it could not reach the vSAN network of the newly added hosts.
  7. Move the added host to the appropriate availability zone so that the cluster is back to containing two fault domains again.
    1. On the SDDC Manager Dashboard, click Inventory > Workload Domains and then click View Details.
    2. Click the name of the domain containing the stretched cluster, for example, MGMT.
    3. Click the Services tab and click the vCenter Server launch icon and log in to the vSphere Web Client.
    4. In the vSphere Web Client, select the stretched cluster. Then select Configure > vSAN > Fault Domains & Stretched Cluster.
    5. Select the first newly added host associated with the network pool on AZ1 and drag it to AZ1.
    6. Select the second newly added host associated with the network pool on AZ2 and drag it to AZ2.
  8. Add these hosts to the VMHost rule so that you can deploy VMs on all hosts.
    1. In the vSphere Web Client, select Hosts and Clusters and then select the stretched cluster.
    2. Select Configure > VM/Host Rules.
    3. Select the <cluster_name> rule and click Add.
    4. Select the ESXi hosts newly added to availability zone 1 and click OK.
  9. Update the value for Host failure cluster tolerates to the number of hosts in AZ1 after the expansion.
    1. Log in to the management vCenter Server in the vSphere Web Client.
    2. From the Home menu, select Hosts and Clusters and expand the stretched cluster.
    3. Select the stretched cluster and click the Configure tab.
    4. Under Services, click vSphere Availability, and click Edit.
    5. On the Admission Control page of the Edit Cluster Settings dialog box, set Host failures cluster tolerates to the number of hosts in AZ1 and click OK.