Re: [DNSOP] HTTP dns-alt-svc draft

[Shumon Huque <[e-mail]>]

On Sat, Jun 23, 2018 at 12:00 AM Shumon Huque <[e-mail]> wrote:

> In other threads, Erik Nygren suggested that we review the proposed
> DNS record for HTTP Alternative Services draft:
>
>     https://tools.ietf.org/html/draft-schwartz-httpbis-dns-alt-svc-02
>     (You might also want to read RFC7838 for background).
>

Another comment on this draft:

I noticed that RFC7838 says:

   The Alt-Svc field value can have multiple values:

   Alt-Svc: h2="alt.example.com:8000", h2=":443"

So, presumably my example in the last message was not quite correct
for representing multiple target hosts for the service:

Instead of:

 _443._https.example.com. 900 IN ALTSVC "h2=\"cdn1.example.org:443\""
 _443._https.example.com. 900 IN ALTSVC "h2=\"cdn2.example.org:8443\""

It probably is:

 _443._https.example.com. 900 IN ALTSVC "h2=\"cdn1.example.org:443\", h2=\"
cdn2.example.org:443\""


It also says:

   When multiple values are present, the order of the values reflects
   the server's preference (with the first value being the most
   preferred alternative).

The preference order of the values does not permit load balancing.
So, if a site wants to do load balancing, as many do today, I assume
they would have to employ only one target hostname, with multiple address
records, and still rely on random/shuffle ordered return of the address
record set from name resolution functions. In this sense, SRV is more
flexible since it supports both priority and proportional load balancing.

Shumon.