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<h1 class="post-title">Fixing Slow Spring Boot Startup</h1>
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<span>Sep 2, 2017</span>
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<h3>TL;DR</h3>
<p>If you are running MacOS, add hostname (output of <code>hostname</code>) to the IPv4 & IPv6 loopback entries in <code>/etc/hosts</code> to cut 10 seconds from Spring Boot startup time.</p>
<h3>The Problem</h3>
<p>Spring Boot has ALWAYS started slow for me.
Almost embarrassingly slow.
How slow?
Start with an empty Spring Boot Web application with Spring Initializer.</p>
<p><img src="/assets/slow-spring-boot-startup/spring-initializer.png" alt="Spring Initializer" /></p>
<p>Now launch the server using <code>./gradlew bootRun</code> and take a look at that launch time.</p>
<p><img src="/assets/slow-spring-boot-startup/bootRun-slow.png" alt="Slow bootRun" /></p>
<p><strong>12.184 seconds!!</strong>
To load nothing but framework.
Yuk!</p>
<p>It turns out as part of Spring Boot startup it makes several calls to <code>InetAddress.getLocalHost().getHostName()</code>, and <a href="https://github.com/spring-projects/spring-boot/issues/7087">this is known to be slow</a>.</p>
<p><a href="https://thoeni.io">Antonio Troina</a> released an awesome <a href="https://thoeni.io/post/macos-sierra-java/">post</a> and <a href="https://github.com/thoeni/inetTester">code sample</a> that highlights the issue.
Running inetTester produced this output:</p>
<p><img src="/assets/slow-spring-boot-startup/inetTester-slow.png" alt="Slow inetTester" /></p>
<p>The <code>InetAddress.getLocalHost().getHostName()</code> call took over 5 seconds.</p>
<h3>The Solution</h3>
<p>A solution exists, and that is to explicitly add your hostname into the IPv4 and IPv6 loopback interface entries in the hosts file.</p>
<p>Before, My standard-ish <code>/etc/hosts</code> file used to look like this:</p>
<p><img src="/assets/slow-spring-boot-startup/etc-hosts-slow.png" alt="Slow etc hosts" /></p>
<p>Here is what my <code>/etc/hosts</code> looks like now:</p>
<p><img src="/assets/slow-spring-boot-startup/etc-hosts-fast.png" alt="Fast etc hosts" /></p>
<p>Now with this change (and no reboot or no terminal restarts), inetTester outputs this:</p>
<p><img src="/assets/slow-spring-boot-startup/inetTester-fast.png" alt="Fast inetTester" /></p>
<p><strong>9 ms!</strong>
Down from 5011 ms.</p>
<p>What effect does this have on Spring Boot's startup time?
Take a look for yourself.</p>
<p><img src="/assets/slow-spring-boot-startup/bootRun-fast.png" alt="Fast bootRun" /></p>
<p><strong>2.264 seconds.</strong>
Down from 12.184 seconds.</p>
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