healthchecks/templates/docs/bash.html

<h1>Shell Scripts</h1>
<p>You can easily add SITE_NAME monitoring to a shell script. All you
have to do is make a HTTP request at an appropriate place in the script.
<a href="https://curl.haxx.se/docs/manpage.html">curl</a> and
<a href="https://www.gnu.org/software/wget/manual/wget.html">wget</a>
are two common command line HTTP clients you can use.</p>
<div class="bash highlight"><pre><span></span><code><span class="c1"># Sends a HTTP GET request with curl:</span>
curl -m <span class="m">10</span> --retry <span class="m">5</span> PING_URL

<span class="c1"># Silent version (no stdout/stderr output unless curl hits an error):</span>
curl -fsS -m <span class="m">10</span> --retry <span class="m">5</span> -o /dev/null PING_URL
</code></pre></div>


<p>Here's what each curl parameter does:</p>
<dl>
<dt><strong>-m &lt;seconds&gt;</strong></dt>
<dd>Maximum time in seconds that you allow the whole operation to take.</dd>
<dt><strong>--retry &lt;num&gt;</strong></dt>
<dd>If a HTTP request fails, retry up to this many times. By default, curl
uses an increasing delay between each retry (1s, 2s, 4s, 8s, ...).
See also <a href="https://curl.haxx.se/docs/manpage.html#--retry-delay">--retry-delay</a>.</dd>
<dt><strong>-f, --fail</strong></dt>
<dd>Makes curl treat non-200 responses as errors.</dd>
<dt><strong>-s, --silent</strong></dt>
<dd>Silent or quiet mode. Hides the progress meter, but also
hides error messages.</dd>
<dt><strong>-S, --show-error</strong></dt>
<dd>Re-enables error messages when -s is used.</dd>
<dt><strong>-o /dev/null</strong></dt>
<dd>Redirect curl's stdout to /dev/null (error messages still go to stderr).</dd>
</dl>
<h2>Signalling Failure from Shell Scripts</h2>
<p>You can append <code>/fail</code> to any ping URL and  use the resulting URL to actively
signal a failure. The following example:</p>
<ul>
<li>runs <code>/usr/bin/certbot renew</code></li>
<li>if the certbot command is successful (exit code 0), sends HTTP GET to <code>PING_URL</code></li>
<li>otherwise, sends HTTP GET to <code>PING_URL/fail</code></li>
</ul>
<div class="bash highlight"><pre><span></span><code><span class="ch">#!/bin/sh</span>

<span class="c1"># Payload here:</span>
/usr/bin/certbot renew
<span class="c1"># Ping SITE_NAME</span>
curl -m <span class="m">10</span> --retry <span class="m">5</span> <span class="s2">&quot;PING_URL</span><span class="k">$(</span><span class="o">[</span> <span class="nv">$?</span> -ne <span class="m">0</span> <span class="o">]</span> <span class="o">&amp;&amp;</span> <span class="nb">echo</span> -n /fail<span class="k">)</span><span class="s2">&quot;</span>
</code></pre></div>


<h2>Logging Command Output</h2>
<p>When pinging with HTTP POST, you can put extra diagnostic information in request
body. If the request body looks like a valid UTF-8 string, SITE_NAME
will accept and store first 10KB of the request body.</p>
<p>In the below example, certbot's output is captured and submitted via HTTP POST:</p>
<div class="bash highlight"><pre><span></span><code><span class="ch">#!/bin/sh</span>

<span class="nv">m</span><span class="o">=</span><span class="k">$(</span>/usr/bin/certbot renew <span class="m">2</span>&gt;<span class="p">&amp;</span><span class="m">1</span><span class="k">)</span>
curl -fsS -m <span class="m">10</span> --retry <span class="m">5</span> --data-raw <span class="s2">&quot;</span><span class="nv">$m</span><span class="s2">&quot;</span> PING_URL
</code></pre></div>


<h2>Auto-provisioning New Checks</h2>
<p>This example uses SITE_NAME <a href="../api/">Management API</a> to create a check "on the fly"
(if it does not already exist) and to retrieve its ping URL.
Using this technique, you can write services that automatically
register with SITE_NAME the first time they run.</p>
<div class="bash highlight"><pre><span></span><code><span class="ch">#!/bin/bash</span>

<span class="nv">API_KEY</span><span class="o">=</span>your-api-key-here

<span class="c1"># Check&#39;s parameters. This example uses system&#39;s hostname for check&#39;s name.</span>
<span class="nv">PAYLOAD</span><span class="o">=</span><span class="s1">&#39;{&quot;name&quot;: &quot;&#39;</span><span class="sb">`</span>hostname<span class="sb">`</span><span class="s1">&#39;&quot;, &quot;timeout&quot;: 60, &quot;grace&quot;: 60, &quot;unique&quot;: [&quot;name&quot;]}&#39;</span>

<span class="c1"># Create the check if it does not exist.</span>
<span class="c1"># Grab the ping_url from JSON response using the jq utility:</span>
<span class="nv">URL</span><span class="o">=</span><span class="sb">`</span>curl -s SITE_ROOT/api/v1/checks/  -H <span class="s2">&quot;X-Api-Key: </span><span class="nv">$API_KEY</span><span class="s2">&quot;</span> -d <span class="s2">&quot;</span><span class="nv">$PAYLOAD</span><span class="s2">&quot;</span>  <span class="p">|</span> jq -r .ping_url<span class="sb">`</span>

<span class="c1"># Finally, send a ping:</span>
curl -m <span class="m">10</span> --retry <span class="m">5</span> <span class="nv">$URL</span>
</code></pre></div>