The “host” is just your friendly name for the connection, not necessarily the hostname of the remote host. You can specify the same username or hostname as many times as you want. My config is made up of mostly blocks like this:
Host server1
HostName server1.you.com
User your_ssh_username
IdentityFile ~/.ssh/yourprivatekey.pem
Host server2
HostName server2.you.com
User your_ssh_username
IdentityFile ~/.ssh/yourprivatekey.pem
The “host” is just your friendly name for the connection, not necessarily the hostname of the remote host. You can specify the same username or hostname as many times as you want. My config is made up of mostly blocks like this: