Re: Redirection to Other IP Addresses

Amos Jeffries <squid3@treenet.co.nz> Tue, 30 July 2019 07:37 UTC

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From: Amos Jeffries <squid3@treenet.co.nz>
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Date: Tue, 30 Jul 2019 19:34:04 +1200
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Subject: Re: Redirection to Other IP Addresses
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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