site/index.html

   1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
   2 <html xmlns="http://www.w3.org/1999/xhtml">
   3 <head>
   4 <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
   5 <title>Project.Mothership</title>
   6 <link href="styles.css" rel="stylesheet" type="text/css" />
   7 <style type="text/css" media="screen">
   8 * {
   9         margin: 0;
  10         font-size: 100%;
  11 }
  12
  13 body {
  14         font: normal .8em/1.5em "Trebuchet MS", Verdana, Arial, Helvetica, sans-serif;
  15         color: #484848;
  16         background: #E6EAE9 url(images/bg_grey.gif);
  17 }
  18
  19 a {
  20         color: #c75f3e;
  21         text-decoration: none;
  22 }
  23
  24 a:hover,
  25 a:active {
  26         text-decoration: underline;
  27 }
  28
  29 #mothership {
  30         width: 307px;
  31         height: 117px;
  32         margin: 0 auto;
  33         background: url(images/god_logo1.gif);
  34 }
  35
  36 #content {
  37         width: 700px;
  38         margin: 3px auto;
  39         background: white;
  40         border: 1px solid #444;
  41         padding: 0 24px;
  42         background: #f8f8ff;
  43         overflow: hidden;
  44 }
  45
  46 .banner {
  47         margin-top: 24px;
  48         border: 1px solid #ddd;
  49         width: 698px;
  50         height: 150px;
  51         background: url(images/banner.jpg);
  52 }
  53
  54 #menu {
  55         margin-top: 5px;
  56 }
  57
  58 #menu div.dots {
  59         background: url(images/red_dot.gif) repeat;
  60         height: 5px;
  61         width: 700px;
  62         font-size: 0;
  63 }
  64
  65 #menu ul {
  66         font-family: "Trebuchet MS", Verdana, Arial, Helvetica, sans-serif;
  67         font-weight: bold;
  68         text-transform: uppercase;
  69         color: #4D4D4D;
  70         font-size: 12px;
  71         padding: 0;
  72         margin: 0;
  73         margin-top: 0 !important;
  74         margin-top: -2px;
  75 }
  76
  77 #menu li {
  78         display: inline;
  79         margin: 0 30px 0 0;
  80 }
  81
  82 #menu a:link,
  83 #menu a:visited {
  84         color: #4D4D4D;
  85         text-decoration: none;
  86 }
  87
  88 #menu a:hover,
  89 #menu a:active {
  90         color: black;
  91         text-decoration: none;
  92 }
  93
  94 #page_home #menu li.menu_home a {
  95         color: #A70000;
  96 }
  97
  98 .columnleft {
  99         float: left;
 100         width: 325px;
 101         margin-bottom: 20px;
 102 }
 103
 104 .columnleft p {
 105                 text-align: justify;
 106 }
 107
 108 .columnright {
 109         float: right;
 110         width: 325px;
 111         margin-bottom: 20px;
 112 }
 113
 114 h1 {
 115         font: bold 1.5em "Trebuchet MS", Verdana, Arial, Helvetica, sans-serif;
 116         color: #f36e21;
 117         text-transform: uppercase;
 118         margin: 1.5em 0 .5em 0;
 119         clear: both;
 120 }
 121
 122 p {
 123         margin-bottom: 1em;
 124 }
 125
 126 ul.features {
 127         padding: 0;
 128         margin-left: 1.5em !important;
 129         margin-left: 1.3em;
 130 }
 131
 132 ul.features li {
 133         list-style-position: outside;
 134         list-style-type: circle;
 135         list-style-image: url(images/bullet.jpg);
 136         line-height: 1.4em;
 137 }
 138
 139 #footer {
 140         text-align: center;
 141         color: white;
 142         margin-bottom: 50px;
 143 }
 144
 145
 146
 147 pre {
 148   line-height: 1.5;
 149   border: 1px solid #ccc;
 150   padding: 1em;
 151   background-color: #efefef;
 152   margin: 1em 0;
 153 }
 154
 155 code {
 156   font-size: 1.2em;
 157 }
 158
 159 .ruby .keywords {
 160   color: blue;
 161 }
 162
 163 .ruby .comment {
 164         color : green;
 165 }
 166
 167 .ruby .string {
 168         color : teal;
 169 }
 170
 171 .ruby .keywords {
 172         color : navy;
 173 }
 174
 175 .ruby .brackets {
 176         color : navy;
 177 }
 178 </style>
 179
 180 <script type="text/javascript" src="javascripts/code_highlighter.js"></script>
 181 <script type="text/javascript" src="javascripts/ruby.js"></script>
 182
 183 </head>
 184
 185 <body id="page_home">
 186
 187 <div id="mothership">
 188
 189 </div>
 190 <div id="content">
 191         <div class="banner">
 192
 193         </div>
 194
 195   <!-- <div id="menu">
 196     <div class="dots"></div>
 197     <ul>
 198       <li class="menu_home"><a href="/">Home</a></li>
 199       <li class="menu_contact"><a href="mailto:tom@projectmothership.com">Contact</a></li>
 200     </ul>
 201     <div class="dots"></div>
 202   </div> -->
 203
 204         <div class="columnleft">
 205                 <h1>A Better Way to Monitor</h1>
 206                 <p>God is an easy to configure, easy to extend monitoring library written in Ruby.</p>
 207                 <p><p>
 208         </div>
 209
 210         <div class="columnright">
 211         <h1>Features</h1>
 212         <ul class="features">
 213                 <li>Config file is written in Ruby</li>
 214                 <li>Write your own conditions in Ruby</li>
 215         </ul>
 216         </div>
 217
 218         <h1>Simple is Better</h1>
 219         <p>Keeping your server processes and tasks running should be a simple part of your deployment process. God aims to be the simplest, most powerful monitoring application available.</p>
 220
 221         <h1>Finally, a Config File that Makes Sense</h1>
 222         <p>The easiest way to understand how god will make your life better is by looking at a sample config file. The following configuration file is what I use at <a href="http://site.gravatar.com/">gravatar.com</a> to keep the mongrels running:</p>
 223
 224 <pre><code class="ruby"># file: gravatar.god
 225 #
 226 # This is the actual config file used to keep the mongrels of
 227 # gravatar.com running.
 228
 229 RAILS_ROOT = "/var/www/gravatar2/current"
 230
 231 God.meddle do |god|
 232   god.interval = 30 # seconds
 233
 234   %w{8200 8201 8202}.each do |port|
 235     god.watch do |w|
 236       w.name = "gravatar2-mongrel-#{port}"
 237       w.cwd = RAILS_ROOT
 238       w.start = "mongrel_rails cluster::start --only #{port}"
 239       w.stop = "mongrel_rails cluster::stop --only #{port}"
 240
 241       pid_file = File.join(RAILS_ROOT, "log/mongrel.#{port}.pid")
 242
 243       w.start_if do |start|
 244         start.condition(:process_not_running) do |c|
 245           c.pid_file = pid_file
 246         end
 247       end
 248
 249       w.restart_if do |restart|
 250         restart.condition(:memory_usage) do |c|
 251           c.pid_file = pid_file
 252           c.above = (150 * 1024) # 150mb
 253           c.times = [3, 5] # 3 out of 5 intervals
 254         end
 255
 256         restart.condition(:cpu_usage) do |c|
 257           c.pid_file = pid_file
 258           c.above = 50 # percent
 259           c.times = 5
 260         end
 261       end
 262     end
 263   end
 264 end</code></pre>
 265
 266 <p>That's a lot to take in at once, so I'll break it down by section and explain what's going on in each.</p>
 267
 268 <pre><code class="ruby">RAILS_ROOT = "/var/www/gravatar2/current"</code></pre>
 269
 270 <p>Here I've set a constant that is used throughout the file. Keeping the <code>RAILS_ROOT</code> value in a constant makes it easy to adapt this script to other applications. Because the config file is Ruby code, I can set whatever variables or constants I want that make the configuration more concise and easier to work with.</p>
 271
 272 <pre><code class="ruby">God.meddle do |god|
 273   god.interval = 30 # seconds
 274
 275   ...
 276 end</code></pre>
 277
 278 <p>The meat of the config file is defined inside a <code>God.meddle</code> block. At this level, you set system wide settings like <code>interval</code>. In this case, we've specified that god should do a check every 30 seconds.</p>
 279
 280 <pre><code class="ruby">  %w{8200 8201 8202}.each do |port|
 281     ...
 282   end</code></pre>
 283
 284 <p>Because the config file is written in actual Ruby code, we can construct loops and do other intelligent things that are impossible in your every day, run of the mill config file. I need to watch three mongrels, so I simply loop over their port numbers, eliminating duplication and making my life a whole lot easier.</p>
 285
 286 <pre><code class="ruby">    god.watch do |w|
 287       w.name = "gravatar2-mongrel-#{port}"
 288       w.cwd = RAILS_ROOT
 289       w.start = "mongrel_rails cluster::start --only #{port}"
 290       w.stop = "mongrel_rails cluster::stop --only #{port}"
 291
 292       ...
 293     end</code></pre>
 294
 295 <p>A <code>watch</code> represents a single process or task that has concrete start, stop, (and possibly restart) operations. You can define as many watches as you like inside the <code>God.meddle</code> block. In the example above, I've got a Rails instance running in a Mongrel that I need to keep alive. Every watch must have a unique <code>name</code> so that it can be identified later on. The optional <code>cwd</code> attribute tells god to switch to that directory before executing any commands. The <code>start</code> and <code>stop</code> attributes specify the commands to start and stop the process. If no <code>restart</code> attribute is set, restart will be represented by a call to stop followed by a call to start.</p>
 296
 297 <pre><code class="ruby">      pid_file = File.join(RAILS_ROOT, "log/mongrel.#{port}.pid")</code></pre>
 298
 299 <p>Another variable to hold the location of the PID file.</p>
 300
 301 <pre><code class="ruby">      w.start_if do |start|
 302         start.condition(:process_not_running) do |c|
 303           c.pid_file = pid_file
 304         end
 305       end</code></pre>
 306
 307 <p>Watches contain conditions grouped by the action to execute should they fail. I start with a <code>start_if</code> block that contains a single condition. Conditions are specified by calling <code>condition</code> with an identifier, in this case
 308 <code>:process_not_running</code>. This condition checks to see if the process corresponding to the PID found in the <code>pid_file</code> is currently running. If it's not, the condition will fail causing a start command to be issued. The <code>process_not_running</code> condition will take care of cleaning up orphaned PID files by default, so we don't have to worry about it. We could turn that behavior off by adding <code>c.clean = false</code>.
 309
 310 <pre><code class="ruby">      w.restart_if do |restart|
 311         restart.condition(:memory_usage) do |c|
 312           c.pid_file = pid_file
 313           c.above = (150 * 1024) # 150mb
 314           c.times = [3, 5] # 3 out of 5 intervals
 315         end
 316
 317         ...
 318       end</code></pre>
 319
 320 <p>Similar to <code>start_if</code> there is a <code>restart_if</code> command that groups conditions that should trigger a restart. The <code>memory_usage</code> condition will fail if the specified process is using too much memory. Once again, the <code>pid_file</code> must be set. The maximum allowable amount of memory is specified with the <code>above</code> attribute in units of kilobytes. The number of times the test needs to fail in order to trigger a restart is set with <code>times</code>. This can be either an integer or an array. An integer means it must fail that many times in a row while an array [x, y] means it must fail x times out of the last y tests.</p>
 321
 322 <pre><code class="ruby">      w.restart_if do |restart|
 323         ...
 324
 325         restart.condition(:cpu_usage) do |c|
 326           c.pid_file = pid_file
 327           c.above = 50 # percent
 328           c.times = 5
 329         end
 330       end</code></pre>
 331
 332 <p></p>
 333
 334 </div>
 335 <div id="footer">
 336         <p>Brought to you by <a href="http://rubyisawesome.com/">Ruby is Awesome</a></p>
 337 </div>
 338
 339 </body>
 340 </html>