Issue
Tableau Server upgrade fails with the following error:
"The primary port for service gateway_0 was already registered on port 80 and cannot be remapped."
or
"UnableToFindAvailablePortException: Port 80 was already registered for port type gateway_0:primary but isn't available. Unable to remap port"
When this error occurred, you might have already set gateway.port to 80 using "tsm topology set-ports" and might have confirmed this using "tsm configuration get -k gateway.port".
You might be able to find that gateway.port is not configured 80 in the configuration file generated by "tsm settings export -f <file name>".