vSAN Unicast Agent List Issue

I had a few problems with my homelab last week after rebuilding one of the hosts in my vSAN cluster. I moved the ESXi install from an increasingly ancient USB drive to an internal SD card. That part was relatively painless. But when I tried to put the “new” host back into the vSAN cluster I ran into issues. It would just not rejoin.

I initially thought I might have knocked a few cables in the change around but vmkpings on all vSAN interfaces checked out so time to run some cli commands.

esxcli vsan cluster get

This gave me the UUID of the vSAN cluster. One of the existing hosts showed 2 members and the rebuild host only 1 but both that the same cluster UUID.

Then I came across the below KB from VMware which made me have a look at the Unicast agent list on the hosts and therein was the problem.

https://kb.vmware.com/s/article/2150303

The rebuilt host entry on the original 2 nodes was not correct, as vCenter was not up the update could not happen automatically, I would have to do it manually.

Firstly confirm the UUID of each node.

cmmds-tool whoami

Check the Unicast Agent list on each host

esxcli vsan cluster unicastagent list

Finally, amend the entries to make sure they are correct (examples below). Important here not to add an entry into the list for the host you are performing the task on – only the other nodes in the cluster. This may even cause a purple screen of death. The agent list must be correct on all hosts in the vSAN cluster.

So add entries for host 2 and host 3 on host 1, entries for host 1 and host 3 on host 2 etc. Consult the KB for further details.

esxcli vsan cluster unicastagent remove -a 10.10.8.101

esxcli vsan cluster unicastagent add -t node -u 5ea08d04-fc58-9af5-96f3-002655e4fef2 -U true -a 10.10.8.101 -p 12321

*Change command to reflect your hosts UUID*

Once the entries were correct on all hosts the rebuilt hypervisor joined the vSAN cluster with no further problems.

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