Re: Clarification on Alternative Service Connection Failures

On Fri, Sep 29, 2017 at 3:03 PM, Patrick McManus <mcmanus@ducksong.com>
wrote:

> On Fri, Sep 29, 2017 at 3:48 PM, Ryan Hamilton <rch@google.com> wrote:
>
>> On Fri, Sep 29, 2017 at 6:27 AM, Patrick McManus <mcmanus@ducksong.com>
>> wrote:
>>
>>> The text is referring to any failure - the client MAY want to try a
>>> different alternative in that case. Its just saying don't feel pinned down
>>> by an Alt-Svc announcement just because you started to use it - you can
>>> always use a different one (or the default) if you think it would work
>>> better. A 500 seems a reasonable input to that choice to me.
>>>
>>
>> ​Wow, really? Hm. While I understand your reasoning here, I don't love it.
>>
>
> I think I should underscore my point - these hosts form a set of
> equivalent alternates. If one of them isn't working well for you - using
> another one is a sensible thing. Errors that seem to be about the host,
> rather than the resource, seem like valid input into that decision. There
> is never a directive that you have to use any particular alternate.. the
> ordering indicates the server's preference but the client is not bound by
> that.
>
>
>> For example, what about 4xx errors?
>>
>
> other than the special case of 421, that's not related to the host or
> connection.. it should be a function of the origin and the request. so I
> wouldn't think that's a reasonable input to the algorithm. But it wouldn't
> be out of spec to panic and flush the alt-svc cache on seeing it (though
> not very helpful either).
>
>
>>   Is it "safe" to advertise an alternative which is not current reachable
>> (I think so).
>>
>
> I think so too. That's definitely a connection error :)
>
>
>> What about one which 404s for all requests, or one which 500s every
>> request? Should this be considered "safe" for a server to advertise?
>>
>
> 500 is an unexpected error on the server, that's pretty different than a
> 404.
>

​Hm. I see your point. I guess I'm accustomed to thinking of 2xx and 3xx
and "good" and 4xx and 5xx as "dammit why is the server broken". (I've seen
404s happening because two different servers behind the same LB were
running out of sync software and depending on which you hit you'd get a 200
or a 404. But that's relatively pathological.)  Semantically I guess 5xx
really is in a different class here. Ok, I'm with you.
http://crbug.com/770379