Re: Redirection to Other IP Addresses

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
>>> >>
>>> >
>>>
>>
>>