You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
112 lines
4.4 KiB
112 lines
4.4 KiB
<h1>Monitoring Cron Jobs</h1>
|
|
<p>SITE_NAME is perfectly suited for monitoring cron jobs. All you have to do is
|
|
update your cron job command to send a HTTP request to SITE_NAME
|
|
after a job completes.</p>
|
|
<p>Let's look at an example:</p>
|
|
<div class="highlight"><pre><span></span>$ crontab -l
|
|
<span class="c1"># m h dom mon dow command</span>
|
|
<span class="m">8</span> <span class="m">6</span> * * * /home/user/backup.sh
|
|
</pre></div>
|
|
|
|
|
|
<p>The above job runs <code>/home/user/backup.sh</code> every day at 6:08. The backup
|
|
script is presumably a headless, background process. Even if it works
|
|
correctly currently, it can start silently failing in future, without
|
|
anyone noticing.</p>
|
|
<p>You can set up SITE_NAME to notify you whenever the backup script does not
|
|
run on time or does not complete successfully. Here are the steps to do that.</p>
|
|
<ol>
|
|
<li>
|
|
<p>If you have not already, sign up for a free SITE_NAME account.</p>
|
|
</li>
|
|
<li>
|
|
<p>In your SITE_NAME account, <strong>add a new check</strong>.</p>
|
|
</li>
|
|
<li>
|
|
<p>Give the check <strong>a meaningful name</strong>. Good naming will become
|
|
increasingly important as you add more checks to your account.</p>
|
|
</li>
|
|
<li>
|
|
<p>Edit the check's <strong>schedule</strong>:</p>
|
|
<ul>
|
|
<li>change its type from "Simple" to "Cron"</li>
|
|
<li>enter <code>8 6 * * *</code> in the cron epression field</li>
|
|
<li>set the timezone to match your machine's timezone</li>
|
|
</ul>
|
|
</li>
|
|
<li>
|
|
<p>Take note of your check's unique <strong>ping URL</strong></p>
|
|
</li>
|
|
</ol>
|
|
<p>Finally, edit your cron job definition and append a curl or wget call
|
|
after the command:</p>
|
|
<div class="highlight"><pre><span></span>$ crontab -e
|
|
<span class="c1"># m h dom mon dow command</span>
|
|
<span class="m">8</span> <span class="m">6</span> * * * /home/user/backup.sh <span class="o">&&</span> curl -fsS --retry <span class="m">3</span> PING_URL > /dev/null
|
|
</pre></div>
|
|
|
|
|
|
<p>Now, each time your cron job runs, it will send a HTTP request to the ping URL.
|
|
Since SITE_NAME knows the schedule of your cron job, it can calculate
|
|
the dates and times when the job should run. As soon as your cron job doesn't
|
|
report at an expected time, SITE_NAME will send you a notification.</p>
|
|
<p>This monitoring technique takes care of various failure scenarios that could
|
|
potentially go unnoticed otherwise:</p>
|
|
<ul>
|
|
<li>The whole machine goes down (power outage, janitor stumbles on wires, VPS provider problems, etc.)</li>
|
|
<li>cron daemon is not running, or has invalid configuration</li>
|
|
<li>cron does start your task, but the task exits with non-zero exit code</li>
|
|
</ul>
|
|
<h2>Curl Options</h2>
|
|
<p>The extra options tells curl to not print anything to standard output unless
|
|
there is an error. Feel free to adjust the curl options to suit your needs.</p>
|
|
<table class="table curl-opts">
|
|
<tr>
|
|
<th>&&</th>
|
|
<td>Run curl only if <code>/home/user/backup.sh</code> exits with an exit code 0</td>
|
|
</tr>
|
|
<tr>
|
|
<th>
|
|
-f, --fail
|
|
</th>
|
|
<td>Makes curl treat non-200 responses as errors</td>
|
|
</tr>
|
|
<tr>
|
|
<th>-s, --silent</th>
|
|
<td>Silent or quiet mode. Don't show progress meter or error messages.</td>
|
|
</tr>
|
|
<tr>
|
|
<th>-S, --show-error</th>
|
|
<td>When used with -s it makes curl show error message if it fails.</td>
|
|
</tr>
|
|
<tr>
|
|
<th>--retry <num></th>
|
|
<td>
|
|
If a transient error is returned when curl tries to perform a
|
|
transfer, it will retry this number of times before giving up.
|
|
Setting the number to 0 makes curl do no retries
|
|
(which is the default). Transient error means either: a timeout,
|
|
an FTP 4xx response code or an HTTP 5xx response code.
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<th>> /dev/null</th>
|
|
<td>
|
|
Redirect curl's stdout to /dev/null (error messages go to stderr,)
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<h2>Looking up Your Machine's Time Zone</h2>
|
|
<p>On modern GNU/Linux systems, you can look up the time zone using the
|
|
<code>timedatectl status</code> command and looking for "Time zone" in its output:</p>
|
|
<div class="highlight"><pre><span></span>$ timedatectl status
|
|
|
|
Local time: C 2020-01-23 12:35:50 EET
|
|
Universal time: C 2020-01-23 10:35:50 UTC
|
|
RTC time: C 2020-01-23 10:35:50
|
|
<span class="hll"> Time zone: Europe/Riga (EET, +0200)
|
|
</span>System clock synchronized: yes
|
|
NTP service: active
|
|
RTC in local TZ: no
|
|
</pre></div>
|