Re: Alt-Svc across a domain?

On Fri, Apr 8, 2016 at 11:01 AM, Patrick McManus <mcmanus@ducksong.com>
wrote:

> On Fri, Apr 8, 2016 at 2:31 PM, Ryan Hamilton <rch@google.com> wrote:
>
>> Howdy,
>>
>> It is common for web sites to serve content from a variety of different
>> origins within the same domain. For example, www.example.com,
>> accounts.example.com, images.example.com. A single page view may require
>> loading resources from several such origins. (Tricks like domain sharing
>> can exacerbate this proliferation of origins.) It would be great if the
>> service had some way to tell the client, "All of my domains can use this
>> alternative service". What would folks thinks of an include-subdomains
>> parameter in the Alt-Svc value? If such a parameter were present in an
>> Alt-Svc advertisement, a client could use this advertisement to apply to
>> any sub-domain of the origin that the client does not already have an
>> alternative for. This would avoid the need to discover the alternatives
>> individually.
>>
>>
> the server can send, unsolicited, on stream 0 an altsvc frame for each
> origin it wants to provide alt-svc info for (the connection needs to be
> authoritative for those origins, of course).
>
> yesterday's discussion of adding certificates to an established connection
> would make that more powerful.
>
> I would encourage h1 servers to update to h2 to get this feature :)
>

Hm. This seems plausible for the simple case where the number of extra
origins is small. But in some cases, the number of extra origins can be ...
enormous.

​In the case of YouTube which I'm quite familiar with, there are literally
thousands of hostnames and they all have the same Alt-Svc. We can't
practically push an origin frame for each server.​ And even if we could, I
suspect that browsers will limit the number of servers for which they are
tracking Alt-Svc information.

Cheers,

Ryan