The Backend section described above can also be used at the
topmost level of the configuration file. Use this if you plan to use
same backend in several different services.
When used globally the Backend keyword must always be
followed by the backend name in double-quotes. The assigned name must
be unique among all global backends.
To include a globally defined backend in a service, use
UseBackend or Backend keywords.
Use globally-defined backend name in this service. The backend
itself may be defined in global scope before or after the
Service section that uses it.
The UseBackend keyword adds the backend to the service exactly
as it was defined. However, it may sometimes be necessary to alter
its priority and state. To do so, use the Backend section. If
the name argument specifies a globally-defined backend, the
Backend section can contain only the Priority and
Disable statements.