A quick post this time, as this is an error that should probably be filed under the RTFM category, but for this reason it could go totally underlooked. Luckily it may be the last time you may face this one, as with vCenter 6.5 now we can finally get rid of the VUM server!
When upgrading the vCenter appliance (VCSA) from 6.0 to 6.5, you may face this error:
Unable to retrieve the migration assistant extension on source vCenter Server. Make sure migration assistant is running on the VUM server
After you enter the required credential in the Windows installer to connect to the existing appliance.
The solution is easy. Mount the VCSA ISO into the Update Manager, and browse the folder called migration-assistant:
Here, run the VMware-Migration-Assistant application and follow the instructions:
As written in bold at the beginning of the tool, DO NOT CLOSE the console until the migration is complete.
Now the VCSA update process can proceed. If you look into this console during the upgrade process, you may see additional messages as the assistant tool is interacting with the upgrade process. Also, remember in the configuration of the upgrade to input the ESXi server that’s managing the previous VCSA, and to set DRS in either manual or partially automated, to be sure that the VCSA will not move from one host to another during the upgrade process.