Host MasterServer
Hostname x
User y
IdentityFile ~/.ssh/id_ed25519
ControlPath ~/.ssh/control-%h-%p-%r # as recommended by the man page
Host MasterServerSQL
Hostname x
User y
IdentityFile ~/.ssh/id_ed25519
LocalForward 3306 localhost:3306
ControlPath ~/.ssh/control-%h-%p-%r
ssh -M MasterServer
ssh -MNf MasterServerSQL
ssh -O exit MasterServer