[PATCH] add documentation about backend naming for VMOD authors

[Dridi Boukelmoune]

>>I don't think it's a good idea to leave the end-user with unnamed
>>backends in the VSL that don't even appear in the CLI and VSM, or
>>confusing names in the CLI/VSM because of name collisions auto-repair.
>
> I think you are thinking far too narrow about backend.
>
> Imagine vmod-cgi.

It's actually on my TODO-unless-someone-starts-before-me list :)

> It would create a backend good only for a single request and it
> doesn't have an IP#, cannot be polled and cannot in any meaningful
> way be set healthy/sick.

But this wouldn't create a backend, only a director with a custom
transport. You wouldn't even get the opportunity for a backend name
conflict.

> Why would you ever name that backend or show it in the CLI ?

That's a director, directors don't show up in the backend.list CLI.

They also don't show up anywhere in varnishstat, and this is a
question I was saving for later because I haven't studied yet whether
you can add out-of-tree VSC fields (at first glance I think not).

Best,
Dridi