Re: Redirection and Load Balancing

On Tue, 30 Jun 1998, Stephen Ollis wrote:

> I'm just curious: what does everyone else use for Redirection
> and Load Balancing on a farm of proxy servers?
>
> I've been looking at the Alteon AceSwitch, which has been getting
> good reviews from around the place.. are there any other contenders?

I don't recall a big response for this issue from the list, but here's my
2c worth.

The Alteon switch is designed to do clustering of like-minded servers in a
redundant and load balanced fashion, and it does this well by acting as a
proxy device (ie: you configure it with a proxy IP address and setup a
load balanced cluster of servers hanging from it).

I've played around with a few different configurations with it, but
haven't yet successfully got it to act as a single point Squid proxy.
What I mean is: it'll load balance TCP/HTTP sessions across multiple
servers fine, but I couldn't get it to forward ICP reliably, since the
proxy ports must be configured along with the proxy IP address.

I tried to solve this issue by configuring a proxy-UDP port to handle ICP
transactions, thinking that the ICP packet would get routed into the
back-end cluster to one of the hosts, who would then ask the other hosts
if they had the object (if that particular host didn't - I hope you get
the picture), but, when the proxy-ICP port was configured, the Squid hosts
couldn't get ICP transactions to one-another. There are a number of ways
around this (that I've thought of) but I haven't got it going yet (viz:
it's not that simple!).

I've discussed this problem with the Alteon dudes, and they acknowledge
that there _is_ a problem and I don't know if they plan to do anything
about it (yet).

This is not to say that the switch won't work with Squid ... it will, and
I believe that the layer-4 feature set (which is expanding at a phenomenal
rate) now includes URL hashing so that if you have multiple cache hosts
hanging of the back end, then the switch will will route URLs to
particular hosts, thereby increasing the hit rate (and decreasing the
load-balancing? was my question, to which I did not get a satisfactory
answer).

Just don't expect to be able to use ICP ... yet.

You should also be warned that although the load balancing features appear
to be a great benefit (as indeed they are when all is well), you are
introducing a single point of failure for a cluster multiple devices.

Sigh ... back to DNS round-robin! :-))

J.

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John V Cougar | Voice: 1800 065 744
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Telstra Internet | E-Mail: cougar@telstra.net
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Received on Thu Aug 06 1998 - 02:27:48 MDT