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<h1>Scaling Node</h1><p>After working through this guide you should be able to</p>
<ul>
<li>set up cluster.js to run several node instances</li>
</ul>
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<h3 class="chapter">
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Chapters
</h3>
<ol class="chapters">
<li><a href="#node-and-the-command-line">Node and the Command Line</a></li>
<li><a href="#arguments">Arguments</a></li>
<li><a href="#standard-input-and-standard-output-channels">Standard Input and Standard Output channels</a></li>
<li><a href="#environment-variables">environment variables</a></li>
<li><a href="#process-id">process id</a></li>
<li><a href="#sending-and-reacting-to-signals">Sending and reacting to signals</a></li>
<li><a href="#scaling-node-with-cluster-js">Scaling Node with cluster.js</a></li>
<li><a href="#see-also">See Also</a></li>
</ol>
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<div class='slide'>
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<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-0' href='slides_node_cluster.html#/0'>◻</a></p>
<h2 id="node-and-the-command-line"><a class="anchorlink" href="#node-and-the-command-line"><span>1</span> Node and the Command Line</a></h2></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-1' href='slides_node_cluster.html#/1'>◻</a></p>
<h2 id="arguments"><a class="anchorlink" href="#arguments"><span>2</span> Arguments</a></h2><p>The array <code>process.argv</code> contains information about how the program
was started:</p><div class="interstitial code">
<pre><code class="highlight plaintext">node fs.js file.txt
</code></pre>
<button class="clipboard-button" data-clipboard-text="node fs.js file.txt
">Copy</button>
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<p>The contents of the array might be:</p><div class="interstitial code">
<pre><code class="highlight plaintext">['/Users/b/.nvm/versions/node/v5.9.0/bin/node', '/Users/b/code/fs.js', 'file.txt' ]
</code></pre>
<button class="clipboard-button" data-clipboard-text="['/Users/b/.nvm/versions/node/v5.9.0/bin/node', '/Users/b/code/fs.js', 'file.txt' ]
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-2' href='slides_node_cluster.html#/2'>◻</a></p>
<h2 id="standard-input-and-standard-output-channels"><a class="anchorlink" href="#standard-input-and-standard-output-channels"><span>3</span> Standard Input and Standard Output channels</a></h2><p>are streams in node:</p><div class="interstitial code">
<pre><code class="highlight javascript"><span class="nx">process</span><span class="p">.</span><span class="nx">stdout</span><span class="p">.</span><span class="nf">write</span><span class="p">(</span><span class="dl">"</span><span class="s2">Hello World</span><span class="se">\n</span><span class="dl">"</span><span class="p">);</span>
<span class="nx">process</span><span class="p">.</span><span class="nx">stderr</span><span class="p">.</span><span class="nf">write</span><span class="p">(</span><span class="dl">"</span><span class="s2">you're doing it wrong</span><span class="dl">"</span><span class="p">);</span>
<span class="nx">console</span><span class="p">.</span><span class="nf">log</span><span class="p">(</span><span class="dl">"</span><span class="s2">this</span><span class="dl">"</span><span class="p">,</span> <span class="kc">true</span><span class="p">,</span> <span class="mi">42</span><span class="p">,</span> <span class="nx">that</span><span class="p">);</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="process.stdout.write("Hello World\n");
process.stderr.write("you're doing it wrong");
console.log("this", true, 42, that);
">Copy</button>
</div>
<div class="interstitial code">
<pre><code class="highlight shell"><span class="nb">node </span>app.js <span class="o">></span> out.txt 2> err.txt
</code></pre>
<button class="clipboard-button" data-clipboard-text="node app.js > out.txt 2> err.txt
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-3' href='slides_node_cluster.html#/3'>◻</a></p>
<h2 id="environment-variables"><a class="anchorlink" href="#environment-variables"><span>4</span> environment variables</a></h2></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-4' href='slides_node_cluster.html#/4'>◻</a></p>
<h2 id="process-id"><a class="anchorlink" href="#process-id"><span>5</span> process id</a></h2><div class="interstitial code">
<pre><code class="highlight javascript"><span class="nx">console</span><span class="p">.</span><span class="nf">log</span><span class="p">(</span><span class="s2">`process </span><span class="p">${</span><span class="nx">process</span><span class="p">.</span><span class="nx">pid</span><span class="p">}</span><span class="s2">`</span><span class="p">)</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="console.log(`process ${process.pid}`)
">Copy</button>
</div>
<p>Or find it on the commandline:</p><div class="interstitial code">
<pre><code class="highlight shell"><span class="nv">$ </span>ps
PID TTY TIME CMD
71422 ttys000 0:00.05 bash
20877 ttys002 0:00.11 <span class="nb">node </span>app.js
</code></pre>
<button class="clipboard-button" data-clipboard-text="$ ps
PID TTY TIME CMD
71422 ttys000 0:00.05 bash
20877 ttys002 0:00.11 node app.js
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-5' href='slides_node_cluster.html#/5'>◻</a></p>
<h2 id="sending-and-reacting-to-signals"><a class="anchorlink" href="#sending-and-reacting-to-signals"><span>6</span> Sending and reacting to signals</a></h2><div class="interstitial code">
<pre><code class="highlight javascript"><span class="nx">process</span><span class="p">.</span><span class="nf">on</span><span class="p">(</span> <span class="dl">"</span><span class="s2">SIGINT</span><span class="dl">"</span><span class="p">,</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">console</span><span class="p">.</span><span class="nf">log</span><span class="p">(</span><span class="s2">`stopping`</span><span class="p">);</span>
<span class="nx">process</span><span class="p">.</span><span class="nf">exit</span><span class="p">();</span>
<span class="p">});</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="process.on( "SIGINT", function() {
console.log(`stopping`);
process.exit();
});
">Copy</button>
</div>
<p>Send SIGINT by pressing CTRL-C
Send SIGINT with <code>kill 20877</code></p><p>SIGTERM is used by docker, always handle it!</p><div class="interstitial code">
<pre><code class="highlight plaintext">process.on( "SIGTERM", function() {
console.log(`stopping`);
process.exit();
});
</code></pre>
<button class="clipboard-button" data-clipboard-text="process.on( "SIGTERM", function() {
console.log(`stopping`);
process.exit();
});
">Copy</button>
</div>
<p>SIGHUB can be used for less serious signals, for example
to get the app to dump some statistics, or reload a configuration file:</p><div class="interstitial code">
<pre><code class="highlight plaintext">let count = 1;
process.on( "SIGHUP", function() {
console.log(`count = ${count}`);
});
</code></pre>
<button class="clipboard-button" data-clipboard-text="let count = 1;
process.on( "SIGHUP", function() {
console.log(`count = ${count}`);
});
">Copy</button>
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<div class="interstitial code">
<pre><code class="highlight plaintext">kill –HUP 20877
</code></pre>
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">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-6' href='slides_node_cluster.html#/6'>◻</a></p>
<h2 id="scaling-node-with-cluster-js"><a class="anchorlink" href="#scaling-node-with-cluster-js"><span>7</span> Scaling Node with cluster.js</a></h2><p>V8 has a default memory limit of ~1.5GB
If your server has more memory
this might be unsatisfactory!
You can increase this by starting node with the option
<code>--max-old-space-size</code>.</p><p>The Eventloop uses 1 core
If your server has 64 cores
this might be unsatisfactory!
To get around this limitation use cluster.js</p><div class="interstitial code">
<pre><code class="highlight plaintext">const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
} else {
console.log('working!');
}
</code></pre>
<button class="clipboard-button" data-clipboard-text="const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
} else {
console.log('working!');
}
">Copy</button>
</div>
<p>sockets are shared between slave processes:</p><div class="interstitial code">
<pre><code class="highlight plaintext">if (cluster.isMaster) {
// ...
} else {
// Workers can share any
// TCP connections
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
}
</code></pre>
<button class="clipboard-button" data-clipboard-text="if (cluster.isMaster) {
// ...
} else {
// Workers can share any
// TCP connections
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
}
">Copy</button>
</div>
<p>the master process is in charge:</p><div class="interstitial code">
<pre><code class="highlight plaintext">if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`${worker.process.pid} died`);
});
}
</code></pre>
<button class="clipboard-button" data-clipboard-text="if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`${worker.process.pid} died`);
});
}
">Copy</button>
</div>
<p>they do not share the same memory space
= objects are local to each instance of the app.
You cannot maintain state in the application code!
You can send messages:</p><div class="interstitial code">
<pre><code class="highlight plaintext">const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
let worker = cluster.fork();
worker.send('do something!');
}
} else {
process.on('message', (msg) => {
process.send('nope.');
});
}
</code></pre>
<button class="clipboard-button" data-clipboard-text="const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
for (var i = 0; i < numCPUs; i++) {
let worker = cluster.fork();
worker.send('do something!');
}
} else {
process.on('message', (msg) => {
process.send('nope.');
});
}
">Copy</button>
</div>
<p>Where do we keep the state of the app? The answers
are the same as for PHP, Rails, etc:</p>
<ul>
<li>in a Database (full featured)</li>
<li>in a key value store like Memcached, Redis (faster, minimal features)</li>
<li>by sending messages</li>
</ul>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-7' href='slides_node_cluster.html#/7'>◻</a></p>
<h2 id="see-also"><a class="anchorlink" href="#see-also"><span>8</span> See Also</a></h2>
<ul>
<li><a href="https://nodejs.org/api/cluster.html">cluster.js documentation</a></li>
<li><a href="https://pm2.io/doc/en/runtime/overview/">pm2 - process manager for Node.js</a></li>
</ul>
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