-----
title: "Book Review: Mongrel Digital Shortcut"
content-type: article
timestamp: 1197686520
tags: "review|books|rails|ruby"
-----
<p>If you ever considered about developing an deploying a Rails application in the last year or so, you must have heard
	of <a href="http://mongrel.rubyforge.org/index.html">Mongrel</a> before. If you didn't, I'd recommend
	you learn more about it because up to now it proved to be one of the few essential ingredients for deploying
	<em>scalable</em> Rails applications.
</p>
<p>Mongrel is a creation of <a href="http://www.zedshaw.com/">Zed Shaw</a> who started writing a replacement for FastCGI
	to use with Rails, and ended up creating a brand new, <span class="caps">HTTP</span> web server who turned out to be
	one of the best things the Rails community ever saw happening.</p>
<p>It was created to be simple to use and configure, nevertheless it <em>does</em> require some skill to set it up and
	tune it. Documentation is there, along with plenty of blog posts, but there's also an interesting <a
		href="http://www.informit.com/store/product.aspx?isbn=0321483502&amp;rl=1">book</a> from <a
		href="http://www.awprofessional.com/">Addison Wesley Professional</a> which is definetely worth a read.</p>
<p style="float:right;"><img src="/images/mongrel_shortcut.jpeg" alt="" /></p>
<p>&#8220;Mongrel: Serving, Deploying, and Extending Your Ruby Applications&#8221; &ndash; that's the title of the
	book. A <em>Digital Shortcut</em>, 100-odd pages long, in <em>landscape</em> format to make it easier to read on a
	computer, straight to the point with no added sugar for just 15$ (<span class="caps">PDF</span> only). I must say
	Addison Wesley got it right: the book's format is, as a matter of fact, <em>optimized for web developers</em>,
	especially those who can't afford to read a 500-pages book covering everything about a subject just to find
	that one thing they don't know about.<br />
	This <em>shortcut</em> can be seen, essentially, as an expanded cheatsheet which will teach you the basics about
	Mongrel and also give you plenty of advice on how to learn more about it.</p>
<p>Let's have a closer look at it.</p>
<h3>Overview, Introduction &amp; Getting Started</h3>
<p>The first three <del>chapters</del> sections (there are no chapters, just <em>sections</em>) of the book are meant to
	be a gentle introduction to Mongrel and its world. The main author is <a
		href="http://www.informit.com/authors/bio.aspx?a=0260912e-6ed8-4ed1-882a-c357e644feec">Matt Pelletier</a>, but
	Zed Show's contributions are definitely one of the book's best selling points. <br />
	Zed's thoughts are scattered here and there in many <em>sidebars</em> throughout the book (there's at
	least one in each section): you'll see an odd-looking face (Zed's self-caricature) with some text next
	to it; when you read it, you'll notice that they are <em>actually</em> Zed's own thoughts, straight from
	his mind, with no editorial filter whatsoever in-between. <br />
	Be warned: the text included within the <strong>Zed Sez</strong> sidebars is highly opinionated, that's
	precisely what Zed <em>feels</em> to say about something, and he'll just say it: just the plain, simple
	thoughts of an experienced programmer. As the author explains in <strong>Section 1</strong>: <em>&#8220;[&#8230;]
		You may not agree with everything he says, but you probably should.&#8221;</em></p>
<p><strong>Section 2</strong> is a general introduction about Mongrel. It explains <em>what</em> it is, <em>when</em>
	and <em>why</em> it was made, and <em>how</em> it works. There's nothing new to learn if you already used
	Mongrel before, probably, but it's definitely the first thing to show to someone who's new to Mongrel
	and its world, and possibly a bit skeptical about it. <br />
	The last subsection <em>&#8220;What can Mongrel do for me&#8221;</em> is an attempt to <del>brainwash</del> persuade
	you to fully embrace Mongrel and its philosophy, whether you are a developer, a sysadmin or even a manager:
	assertions like <em>&#8220;Mongrel is pretty damned secure.&#8221;</em> and <em>&#8220;Mongrel's license is
		capitalist-friendly.&#8221;</em> will definitaly make some of you (managers) happy.</p>
<p><strong>Section 3</strong> is slightly more juicy than the previous one, as it explains how to install and use
	Mongrel. Basically that's what everyone who ever used it already knows, but it's still necessary for the
	book's consistency, after all. After reading this section, you'll probably have your first Mongrel up
	and running and serving your little Rails application's pages, and you'll begin to wonder why the hell
	you need to keep reading this book now that everything seems to work already&#8230;</p>
<h3>Section 4: Configurations</h3>
<p>&#8230;aka &#8220;a truly useful Mongrel cheatsheet&#8221;. This section dives deep(er) into Mongrel's
	configuration by explaining what each start parameter does in detail. The parameters are presented in tabular form
	in a very well-organized way. As you would expect from an high-quality cheatsheet.</p>
<p>Then the author will explore a few commonly used deployment scenarios, in particular:</p>
<ul>
	<li><strong>Standalone</strong> &ndash; The simplest configuration possible, with just one Mongrel instance serving
		both static and dynamic pages.</li>
	<li><strong>mongrel&#95;cluster</strong> &ndash; How to use <em>&#8220;a pack of mongrels&#8221;</em> together to
		handle more traffic.</li>
	<li><strong>Behind a static web server</strong> &ndash; The most common (and most scalable) option, used to serve
		static content faster using a front-end server and use Mongrel only to handle Ruby pages.</li>
</ul>
<p>Towards the end of the section, for the developer's delight, the author will discuss two common, useful
	scenarios where Mongrel can be used:</p>
<ul>
	<li><strong>Apache 2 + mod_proxy_balancer + mongrel&#95;cluster</strong></li>
	<li><strong>Nginx + mongrel&#95;cluster</strong></li>
</ul>
<p>The difference here is that detailed instructions are provided on how to setup and configure each server, including
	example file sources. This can be particularly useful for the Nginx example, as most of the documentation for this
	fantastic, lightweight Mongrel fron-end is scattered around the web (or written in Russian in a <a
		href="http://sysoev.ru/nginx/">well known place</a>).</p>
<h3>Section 5: Production Deployment</h3>
<p>This section introduces one of the most important part of the life cycle of a Rails application: the deployment on a
	production server. The author is pretty honest about the whole subject:</p>
<blockquote>
	<p><em>&#8220;You will not do this in a day. If you are expecting to code until 1 minute before your deadline and
			then simply point and click and have an instant server then you need to take some kind of<br />
			medication because you are violently hallucinating. You will need at least a week of 8 hours days to make
			sure your first deployment works and to have the time to do it right.&#8221;</em></p>
</blockquote>
<p>Sounds terribly true. Especially for larger projects demanding good performance under heavy traffic. Scared?
	Probably, if you never deployed a Rails application &#8220;properly&#8221; before, but at least the book comes to
	the rescue by providing an overview of what you need to perform a deployment and why it is such a complex and
	delicate process.</p>
<p>Not only this, but also a &#8220;Best Practices Rubric&#8221; is also provided for the developer's own private
	enjoyement. It's written as a list of questions like:</p>
<p><em>11. Do you have a shared location where you can document the deployment, such as a Wiki or <span
			class="caps">CMS</span>?</em><br />
	<em>12. Do you know how to use httperf or ab and know what the statistics mean?</em>
</p>
<p>After these 13 questions, the author provides the key to give a meaning to your answers:</p>
<blockquote>
	<p><em>&quot;For each question you answer with &#8220;NO&#8221;, add 10 hours to your time estimate for completion.
			This may seem unrealistic, since saying &#8220;NO&#8221; to everything means it'll take 190 hours
			(about one<br />
			month), but this estimate is actually low according to most first deployment experiences.&quot;</em></p>
</blockquote>
<p>If you answered &#8220;NO&#8221; too many times to these questions, you may want to read on through the next
	subsection which states 17 &#8220;worst practices&#8221;: an invaluable read for beginners!</p>
<p>But after all this section is not only about stating the obvious (&#8230;right?): a full example scenario is
	describedand examined throughly to give you an idea of how a deployment <em>should</em> be made, using three
	different machines:</p>
<ul>
	<li>One for Apache (as a front-end to Mongrel)</li>
	<li>One for the Mongrel cluster and the Rails application</li>
	<li>One for the database</li>
</ul>
<p>Maybe something you'll never do if you just want to run your grandma's site on Rails, but certainly
	something you may want to start looking at if your grandma becomes really popular and your small server gets
	grounded by several thousands of visitors per day.</p>
<p>The last part of the section will give you a brief introduction on monitoring your applications and on which tools
	you should be using, although it does not discuss the subject in detail at all, it's just meant to point you
	to the right direction.</p>
<h3>Section 6: Extending Mongrel</h3>
<p>This section digs deeper into the software code internals and describes <em>how to teach new tricks to your
		Mongrel</em>, i.e. how to extend its functionality.</p>
<p>Before you begin, though, don't forget what Zed himself has to say about Mongrel's simplicity:</p>
<blockquote>
	<p><em>&#8220;I've always had a different aesthetic sense when I write my software. I value simplicity and
			directness and try to write software that follows this approach. I jokingly call it the Shibumi School of
			Software Structure. All I do is apply this rule: When given two possible designs with equal end results,
			pick the simpler one. I then ruthlessly strip the solution down to its finest elements, but no
			more.&#8221;</em></p>
</blockquote>
<p>Mongrel's architecture is not that complex, and this section is sufficient to get you started by providing an
	overview of the main classes involved (HttpServer, HttpRequest, HttpResponse, HttpHandler, URIClassifier), and how
	they work together.<br />
	Note that the book won't describe anything about the APIs of these classes. but after all, the project's
	<a href="http://mongrel.rubyforge.org/rdoc/files/README.html">RDoc documentation</a> should cover all the details
	you need.
</p>
<p>The rest of the section focuses on how to extend Mongrel, by:</p>
<ul>
	<li>Writing custom handlers in Ruby</li>
	<li>Creating custom filters to perform security checks, clean up requests and preliminary file processing</li>
	<li>Creating plugins and distributing them as rubygems</li>
</ul>
<p>Two working examples are also provided:</p>
<ul>
	<li>An example handler to deflate content (if the browser supports deflate)</li>
	<li>An example &#8220;duck&#8221; plugin, to make Mongrel quack like a duck when it's started (not the most
		useful thing in the world, but serves the purpose)</li>
</ul>
<h3>Debugging, Performance &amp; Security</h3>
<p>The last three sections deals with other important aspects concerning the deployment of your application, how to
	debug, how to improve performance and how to secure your application.</p>
<p><strong>Section 7</strong> introduces two debugging modes:</p>
<ul>
	<li>Dash-Bee logging (-B)</li>
	<li>USR1 logging (lighter)</li>
</ul>
<p>And also gives you an idea on what to look for when debugging an application. Nothing too detailed, granted, but
	enough to make sure you are pointed in the right direction.</p>
<p>Again, Zed's wisdom and wit are remarkable:</p>
<blockquote>
	<p><em>&#8220;These people's problem is they suffer from Potpourri Turd Syndrome—a belief that their
			you-know-what don't stink and smells like fine dew on freshly cut grass. Whenever there's a bug,
			they go<br />
			running like kids in a candy store to other people's code trying to find fault and just assume that
			it's nothing they wrote.<br />
			[&#8230;]<br />
			When you run into a problem with your application, always assume it's your fault first.
			Mongrel's not perfect, but its code is minuscule compared to the size of Rails and most likely even
			your own appli-cation code. Mongrel also powers many large and medium deployments without any problems. If
			there's an error, the evidence already says it's in your code, so bite the bullet and start
			investigating it as if it's your problem.&#8221;</em></p>
</blockquote>
<p>Similarly, <strong>Section 8</strong> is a short but useful overview on performance tips and tricks and deployment
	tuning. The most useful thing is probably the checklist of the &#8220;tuning process&#8221;, which illustrates the
	simple steps to take to tune your application.</p>
<p>Finally, <strong>Section 9</strong> addresses some common security concerns and clarifies how Mongrel deals with
	them. The answer is normally &#8220;Mongrel strictly does this&#8221; or &#8220;Mongrel doesn't support this
	feature&#8221;. After all, you should have understood by now that Mongrel is an example of simplicity and that it
	deliberately does not aim to offer all the feature you'd expect by a server like Apache:</p>
<blockquote>
	<p><em>&quot;As you probably see, Mongrel say, &#8220;No&#8221; in many places where most Web servers say,
			&#8220;Yes, OK.&#8221; Sometimes this is because no one using Mongrel has needed it yet, sometimes
			it's because there's a<br />
			better, simpler way to accomplish the same goal. Mongrel is a different kind of Web server, and frequently
			you can solve your problem with a different solution.&quot;</em></p>
</blockquote>
<h3>Conclusion</h3>
<p>If Mongrel is opinionated software, this is definitely an opinionated book which fully embraces the project's
	philosopy of simplicity above everything else. It's an interesting read and it won't bore you to death
	by deliberately skipping long and potentially tedious subjects and adding interesting insights instead (like the Zed
	Sez sidebars). Perhaps it is a bit too direct towards certain people, who may get even get offended (as planned) by
	some of the author's assertions.</p>
<p>Despite being a 100-pages book, this <em>shortcut</em> covers pretty much everything you need to know <strong>about
		Mongrel</strong>. It will <em>not</em> teach you everything about deployment, security, performance tweaks and
	debugging though: as the authors often state throughout the book, a lot of (big) books are available on those
	subject, and it wouldn't make sense to even attempt to discuss them in this shortcut.</p>
<p>Similarly, you won't find complex examples either, but that's acceptable because simple examples are
	often the only thing you need to grasp the basics of a concept or feature, and then use them as a
	&#8220;scaffold&#8221; for your own code.</p>
<p>Globally, the book is well balanced and <em>optimized</em> for its size: lightweight introductory sections at first,
	then the &#8220;real juice&#8221; in the middle, and a few overview sections on advanced topics towards the end. You
	can read it easily in a few hours, perhaps less, and whenever you need to look something up in a hurry it will be
	fairly easy to locate.</p>
<p>A good read, and a <em>must</em> for everyone who wants to learn more about Mongrel or Rails deployment.</p>