Re: Redirection to Other IP Addresses

>
> Versus with "alt-svc", the server will serve the content for the current
> request, client will finish receiving the response and MAYBE connect to the
> new IP for the next request.


Could you return a 4xx error with the Alt-Svc header set, and a body
message that tells clients they must use the Alt-Svc if they don't want to
get a 4xx? Or even a generic 300? It seems reasonable to me for a CDN
server to refuse to serve requests it knows will be prohibitively
expensive, while providing clients with Alt-Svc as a way to find a
less-expensive alternative.

On Wed, Jul 31, 2019 at 8:55 PM Bin Ni <nibin@quantil.com> wrote:

> Hi Chris,
>
> There are a few caveats in your reasoning:
> 1.  It does not have to be some "accept header". It can be the
> "User-Agent" header as I mentioned, for example, chrome version > 100. Or
> on contract. For example, some CDN customers have full control of the
> client software. They just tell the CDN provider that "you can enable the
> 312 redirection on all of our domains".
> 2. Even when it does rely on some "accept header", there is still a
> critical difference from "alt-svc":
>     In this proposal, the current request will not be served. The client
> will get a 312 and forced to reconnect to the new IP, similar to the 30X
> redirection.
>     Versus with "alt-svc", the server will serve the content for the
> current request, client will finish receiving the response and MAYBE
> connect to the new IP for the next request.
>
> Hope this is more clear. Please don't hesitate with more questions!
> Thanks!
>
> Bin
>
> On Wed, Jul 31, 2019 at 6:49 PM Chris Lemmons <alficles@gmail.com> wrote:
>
>> So, the typical mechanism for that would be an accept header of some
>> sort. But if clients are opting into the redirect, then the redirect is
>> effectively optional. Any client that would set the accept header can
>> instead just support alt-svc today and choose to redirect.
>>
>> On Wed, Jul 31, 2019 at 7:39 PM Bin Ni <nibin@quantil.com> wrote:
>>
>>> Hi Chris,
>>>
>>> Great question!
>>> The solution is that the server will only return the new status code 312
>>> if it is sure the client can support it.
>>> The information can be from the User-Agent header, or some other request
>>> header.
>>> Or communicated through some other channel, for example, on a paper
>>> contract.
>>>
>>> Thanks!
>>>
>>> Bin
>>>
>>>
>>> On Wed, Jul 31, 2019 at 2:36 PM Chris Lemmons <alficles@gmail.com>
>>> wrote:
>>>
>>>> So I have to wonder about the end usefulness from an implementation
>>>> perspective. Part of why alt-svc works is that it's optional, so
>>>> servers can use them as optimization but everything else still works.
>>>>
>>>> If you have a new protocol that means basically "alt-svc, but
>>>> mandatory", it means the CDN, load balancer, or similar service simply
>>>> wouldn't work for any client that didn't understand the new value.
>>>> There are a _lot_ of http clients out there. This would be a fairly
>>>> high barrier to adoption, which would create a chicken-and-egg problem
>>>> that would be tough to solve.
>>>>
>>>> On Tue, Jul 30, 2019 at 5:53 PM Bin Ni <nibin@quantil.com> wrote:
>>>> >
>>>> > Hi Amos and All,
>>>> >
>>>> > Regarding the 30X redirect across different cache servers, it is
>>>> already used by many big CDN companies that I know of.
>>>> > It is proven to make the system faster without much burden on the
>>>> front-end layer which you are concerned.
>>>> > But 30X has the limitations I mentioned. This is why I'm proposing
>>>> this new type of redirection to address the limitations.
>>>> >
>>>> https://docs.google.com/document/d/1gtF6Nq3iPe44515BfsU18dAxfCYOvQaekiezK8FEHu0/edit?usp=sharing
>>>> > So it is not a question that this proposal will be useful or not.
>>>> > I know it will at least be very useful to those CDNs.
>>>> >
>>>> > Thanks for your comments.
>>>> > Please let me know if you have any questions.
>>>> >
>>>> > Bin
>>>> >
>>>> > On Tue, Jul 30, 2019 at 12:38 AM Amos Jeffries <squid3@treenet.co.nz>
>>>> wrote:
>>>> >>
>>>> >> On 30/07/19 7:02 am, Bin Ni wrote:
>>>> >> > Yes, what we want is a way to force a "deterministic behavior from
>>>> the
>>>> >> > client", just like all the 30X redirections today.
>>>> >> >
>>>> >> > Let me give a few more cases in which this can be helpful:
>>>> >> > 1. A client in North America is returned a server IP in Europe by
>>>> the
>>>> >> > DNS. The server then wants to direct the client to another server
>>>> in
>>>> >> > North America for better performance.
>>>> >> > 2. The content of a website is hashed to multiple servers based on
>>>> URL.
>>>> >> > These multiple servers may not even be in the same datacenter. The
>>>> DNS
>>>> >> > does not have this information and may return any IP to any query
>>>> of the
>>>> >> > website's hostname.  Each server will calculate the hash for each
>>>> >> > request and redirect client to the correct server that has the
>>>> content.
>>>> >> > This is quite common for CDN.
>>>> >>
>>>> >> It is common for good reason: efficiency.
>>>> >>
>>>> >> There is a secondary level of efficiency that comes from the
>>>> redirects
>>>> >> being actual HTTP 30x redirects. Having large objects at different
>>>> URL
>>>> >> entirely provides for a different CDN or caching layer closer to the
>>>> >> client to provide the large object contents. DNS can be (often is)
>>>> >> involved in that layer to provide the closest server IP.
>>>> >>
>>>> >> As proposed so far your mechanism would flatten this two-tier
>>>> structure.
>>>> >> Forcing the frontend layer (now only layer) to be involved in
>>>> deciding
>>>> >> the specific hardware location of individual objects / resources.
>>>> >>  Making the frontend machinery store more information and do more
>>>> work
>>>> >> per-request is not going to make the system faster, quite the
>>>> opposite.
>>>> >>
>>>> >>
>>>> >> By separating the work into the three layers: frontend LB, cache, and
>>>> >> origin. Each CDN layer gets some orders of magnitude increase in
>>>> >> performance / capacity:
>>>> >>  - origin able to handle/generate some few thousand responses per
>>>> second,
>>>> >>  - cache able to re-distribute those as static objects at line speed
>>>> for
>>>> >> an order or two magnitude more than origins,
>>>> >>  - frontend LB able to handle millions of the small ~1KB
>>>> >> request/response pairs for redirection spreading that high load
>>>> across
>>>> >> the lower layers.
>>>> >>
>>>> >>
>>>> >> AYJ
>>>> >>
>>>> >
>>>>
>>>
>>>