Re: Redirection to Other IP Addresses

Chris Lemmons <> Wed, 31 July 2019 21:38 UTC

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From: Chris Lemmons <>
Date: Wed, 31 Jul 2019 15:36:00 -0600
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To: Bin Ni <>
Cc: Amos Jeffries <>, HTTP Working Group <>
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Subject: Re: Redirection to Other IP Addresses
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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 <> 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.
> 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 <> 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