Re: Redirection to Other IP Addresses

Bin Ni <> Mon, 29 July 2019 19:05 UTC

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From: Bin Ni <>
Date: Mon, 29 Jul 2019 12:02:29 -0700
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To: Kyle Rose <>
Cc: Ben Schwartz <>, "Oliver, Wesley, Vodacom South Africa (External)" <>, Julian Reschke <>, Ryan Hamilton <>, "" <>
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Subject: Re: Redirection to Other IP Addresses
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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.

Usually this kind of redirection is applied to large objects, where the
overhead of one more round trip is negligible.


On Mon, Jul 29, 2019 at 7:48 AM Kyle Rose <> wrote:

> On Mon, Jul 29, 2019 at 9:46 AM Ben Schwartz <> wrote:
>> On Mon, Jul 29, 2019 at 3:40 AM Oliver, Wesley, Vodacom South Africa
>> (External) <> wrote:
>>> Hi,
>>> I would like to suggest, that this not be a specific response code, like
>>> a
>>> 312 or 302. That it just be a response header, that gets checked by
>>> Inteligent clients, would then always check for the new address and port
>>> on which to contact the server,
>> You're in luck: this is precisely the Alt-Svc header (RFC 7838).  You can
>> use this today!
>> Not all clients currently implement full support for this header, but
>> hopefully that will improve over time.
> I think the issue OP is raising is that they want some deterministic
> behavior from the client, dictated by the server. Alt-Svc doesn't do this:
> it's advisory. As a result, it can be used as an optimization, but some
> kind of load balancer for the original service is still required for
> clients that do not react to Alt-Svc (should that population be large
> enough), or when the target Alt-Svc is down. As long as that's within OP's
> constraints, I agree Alt-Svc is precisely the right solution.


Bin Ni
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