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nationalparks-java-application-health.html
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<!DOCTYPE html>
<html>
<head>
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<!-- Header -->
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<!-- Title -->
<h1 class="title">Application Health</h1>
<!-- Content -->
<div class="sect1">
<h2 id="_background_readiness_and_liveness_probes">Background: Readiness and Liveness Probes</h2>
<div class="sectionbody">
<div class="paragraph">
<p>As we have seen before in the UI via warnings, there is a concept of application
health checks in OpenShift. These come in two flavors:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Readiness probe</p>
</li>
<li>
<p>Liveness probe</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>From the
<a href="https://docs.openshift.com/container-platform/latest/applications/application-health.html">Application
Health</a> section of the documentation, we see the definitions:</p>
</div>
<div class="dlist glossary">
<dl>
<dt>Liveness Probe</dt>
<dd>
<p>A liveness probe checks if the container in which it is configured is still
running. If the liveness probe fails, the kubelet kills the container, which
will be subjected to its restart policy. Set a liveness check by configuring
the <code>template.spec.containers.livenessprobe</code> stanza of a pod configuration.</p>
</dd>
<dt>Readiness Probe</dt>
<dd>
<p>A readiness probe determines if a container is ready to service requests. If
the readiness probe fails a container, the endpoints controller ensures the
container has its IP address removed from the endpoints of all services. A
readiness probe can be used to signal to the endpoints controller that even
though a container is running, it should not receive any traffic from a proxy.
Set a readiness check by configuring the
<code>template.spec.containers.readinessprobe</code> stanza of a pod configuration.</p>
</dd>
</dl>
</div>
<div class="paragraph">
<p>It sounds complicated, but it really isn’t. We will use the web console to add
these probes to our <code>nationalparks</code> application.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_exercise_add_health_checks">Exercise: Add Health Checks</h2>
<div class="sectionbody">
<div class="paragraph">
<p>As we are going to be implementing a realistic CI/CD pipeline, we will be doing
some testing of the "development" version of the application. However, in order
to test the app, it must be ready. This is where OpenShift’s application health
features come in very handy.</p>
</div>
<div class="paragraph">
<p>We are going to add both a readiness and liveness probe to the existing
<code>nationalparks</code> deployment. This will ensure that OpenShift does not add any
instances to the service until they pass the readiness checks, and will ensure
that unhealthy instances are restarted (if they fail the liveness checks).</p>
</div>
<div class="paragraph">
<p>From the <strong>Topology</strong> view, click <code>nationalparks</code>. On the side panel, click the <strong>Actions</strong> dropdown menu and the select <strong>Add Health Checks</strong>.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="images/nationalparks-application-health-menu.png" alt="Add Health Checks">
</div>
</div>
<div class="paragraph">
<p>Click to <strong>Add Readiness Probe</strong> and add in <strong>Path</strong> field:</p>
</div>
<div class="listingblock copypaste">
<div class="content">
<pre class="highlight"><code>/ws/healthz/</code></pre>
</div>
</div>
<div class="paragraph">
<p>Leave all default settings like <strong>Port</strong> 8080 and <strong>Type</strong> HTTP GET. Click the little bottom-right confirmation gray tick to confirm:</p>
</div>
<div class="imageblock">
<div class="content">
<img src="images/nationalparks-application-health-settings.png" alt="Add Readiness and Liveness Probe">
</div>
</div>
<div class="paragraph">
<p>Repeat the same procedure for Liveness Probe, click to <strong>Add Liveness Probe</strong> and add in <strong>Path</strong> field:</p>
</div>
<div class="listingblock copypaste">
<div class="content">
<pre class="highlight"><code>/ws/healthz/</code></pre>
</div>
</div>
<div class="paragraph">
<p>Leave all default settings like <strong>Port</strong> 8080 and <strong>Type</strong> HTTP GET. Click the little bottom-right confirmation gray tick to confirm.</p>
</div>
<div class="admonitionblock warning">
<table>
<tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">
Note the trailing slash in the URL
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Finally confirm all new changes clicking to <strong>Add</strong>:</p>
</div>
<div class="imageblock">
<div class="content">
<img src="images/nationalparks-application-health-add.png" alt="Add Probes">
</div>
</div>
<div class="paragraph">
<p>You will notice that these changes caused a new deployment — they counted as a
configuration change.</p>
</div>
</div>
</div>
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