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Squid: The Definitive Guide Duane Wessels
Published by O'Reilly Media
464 pages
£ 31.95
Published: 13th February 2004
reviewed by Mike Smith
   in the June 2004 issue (pdf), (html)

This is a very good book, covering the basics of Squid all the way through to some fairly advanced topics. It is in a pretty standard format -- similar to other O'Reilly texts on software packages. The first three chapters provide some context and how to obtain, compile and install Squid. I hadn't realised that NetApp's NetCache has the same code base, originating from the Harvest project. Each chapter has a few exercises at the end. I presume Duane is still in education and intends for each of his students to buy a copy - a common trick!

Naturally, on the cover there is a picture of ... a squid! Apparently they can grow to 60 feet in length, weigh up to a ton, and their eyes can be as much as 10 inches in diameter. The Colophon is always worth a read.

Anyway, chapter four is a good inclusion in the book - a getting started quick section. i.e. what the essential configuration parameters are to get you going. The full list of parameters is eventually covered over a number of chapters, organised into a number of subjects (such as access control, disk caching etc) - thankfully the book isn't just an alphabetical list of these parameters and an associated explanation. In fact appendix A is a reference for all configuration parameters.

There's a section on how to setup interception (transparent) caching. Although this is, in the main, not about Squid itself, obviously you need to know how to setup IPChains/IPTables and other mechanisms (for instance configurations for Alteon, Extreme, Cisco and other devices are briefly documented) to support a caching service. Its worthwhile having, but because it tries to cover so many routing appliances, it's a little scant on detail.

Things get more interesting when there are multiple caching servers involved. This isn't something I've done myself - I've only used a simple single-server configuration to avoid using work's official Internet gateway in the past ;-) The mechanics of setting up ICP (and other protocols) are covered, but I would have welcomed a more thorough discussion on the ``macro'' architecture of caching services - by that I mean the overall topology. For instance, in a large network environment with multiple external gateways in different locations, would it be best to distribute the caching service, with servers near to the firewalls (in network terms) of have a single centralised farm? Please write in to the magazine if you know - but I suspect the answer is ymmv. There could have been more diagrams in this area, for instance to describe various hierarchical, peering and load-balancing options too.

There's a brief chapter on Squid Redirectors, which looks like an interesting feature. Never used it. There is, again a brief, chapter on Authentication. This just covers the Squid aspects rather than a full explanation of an entire implementation. So just that you need to configure and compile in the helper programs, and use various configuration file options to use them.

Another tool that I haven't used, but looks extremely useful is the Cache Manager. This has web and command line interfaces for monitoring Squid's performance. Statistics are maintained for all manner of metrics including DNS resolution times, disk IO, memory and network utilisation. I'm not sure how well it would tie together the statistics from a cache farm or hierarchy - but I suspect that's another exercise for the interested reader.

I'm most interested in the datacentre environment, and chapter 15 covers one area that can be really useful - Server Acceleration. There are some specific configuration parameters to deal with this, and some restrictions. Good to see it documented.

So in summary, as I opened the review with, it's a good book and recommended, but lacking in some areas - particularly in the design of caches with multiple caching servers. Maybe that's in Duane's other O'Reilly book, ``Web Caching'' - I really ought to review that!

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