Re: Redirection to Other IP Addresses

Bin Ni <nibin@quantil.com> Thu, 01 August 2019 07:33 UTC

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From: Bin Ni <nibin@quantil.com>
Date: Thu, 1 Aug 2019 00:30:18 -0700
Message-ID: <CAFifEM+j1njr1cmetby8cjprrbgn=gfjtgqBsgyypS44rUn7fQ@mail.gmail.com>
To: Jack Firth <jackhfirth@gmail.com>
Cc: Chris Lemmons <alficles@gmail.com>, Amos Jeffries <squid3@treenet.co.nz>, HTTP Working Group <ietf-http-wg@w3.org>
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Subject: Re: Redirection to Other IP Addresses
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Hi Jack,

Actually, 300 was also my first reaction when Julian brought up "alt-svc".
Technically, the main benefit of using a new status code vs reusing an
existing status code is easier statistics.
People can tell what happened by only look at the status code in the access
log.
I think this is the main purpose of defining different status code in the
first place.

Bin


On Thu, Aug 1, 2019 at 12:07 AM Jack Firth <jackhfirth@gmail.com>; wrote:

> Yes you could make a status code, but I don't follow why you need a new
> status code instead of reusing a generic 300 response with body explaining
> they need to follow Alt-Svc. A special status code requires clients to
> implement new behavior, and if they're doing that already can't they just
> implement Alt-Svc support instead? As for 4xx, it sounds like a client
> error to me in the same way that 429 Too Many Requests is: the client asked
> for something correctly, but did so in a way that places too great a burden
> on the server.
>
> On Thu, Aug 1, 2019 at 12:03 AM Bin Ni <nibin@quantil.com>; wrote:
>
>> Hi Jack,
>>
>> Potentially, we can extend RFC 7838, as I mentioned in my proposal
>> <https://docs.google.com/document/d/1gtF6Nq3iPe44515BfsU18dAxfCYOvQaekiezK8FEHu0/edit#heading=h.e8fyx0s8f7wy>;,
>> to define the behavior of client and server when "alt-svc" is used in
>> conjunction with a special status code. This is still a change/extension to
>> the existing protocol. I feel 4xx is not good for this purpose, since this
>> is not a client error. I think a 3XX is more appropriate.
>>
>> Thanks!
>>
>> Bin
>>
>> On Wed, Jul 31, 2019 at 10:52 PM Jack Firth <jackhfirth@gmail.com>; wrote:
>>
>>> 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
>>>>>>> >>
>>>>>>> >
>>>>>>>
>>>>>>
>>>>>>
>>
>> --
>>
>> Bin Ni
>> VP of Engineering
>> [image: Quantil]
>>
>> Connecting users with content...it's that simple.
>>
>> Office: +1-888-847-9851 <(888)%20847-9851>
>>
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>>
>>

-- 

Bin Ni
VP of Engineering
[image: Quantil]

Connecting users with content...it's that simple.

Office: +1-888-847-9851 <(888)%20847-9851>

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or visit our website at www.quantil.com. <https://www.quantil.com/>