{% extends "base.html" %}
{% load staticfiles %}

{% block title %}Documentation - healthchecks.io{% endblock %}

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<div class="row"><div class="col-sm-12">

<h2>Summary</h2>
<p>
Each check you create in <a href="{% url 'hc-index' %}">My Checks</a>
page has an unique "ping" URL. Whenever you access this URL,
the "Last Ping" value of corresponding check is updated.
</p>
<p>When a certain amount of time passes since last received ping, the
check is considered "late", and Health Checks sends an email alert.
It is all very simple, really.</p>

<h2>Executing a Ping</h2>
<p>
    At the end of your batch job, add a bit of code to request
    your ping URL.
</p>
<ul>
    <li>HTTP and HTTPS protocols both are fine</li>
    <li>Request method can be GET, POST or HEAD</li>
    <li>Both IPv4 and IPv6 work</li>
    <li>It does not matter what request headers you send</li>
    <li>You can leave request body empty or put anything in it, it's all good</li>
</ul>

<p>The response will have status code "200 OK" and response body will be a
short and simple string "OK".</p>

<p>
    Here are examples of executing pings from different environments.
</p>

<h3>Crontab</h3>

<p>
When using cron, probably the easiest is to append a <code>curl</code>
or <code>wget</code> call after your command. The scheduled time comes,
and your command runs. After it completes, the healthchecks.io check
gets pinged.
</p>

{% include "front/snippets/crontab.html" %}

<p>With this simple modification, you monitor several failure
scenarios:</p>

<ul>
    <li>The whole machine has stopped working (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>

<p>Either way, when your task doesn't finish successfully, you will soon
know about it.</p>


<h3>Bash or a shell script</h3>

<p>Both <code>curl</code> and <code>wget</code> examples accomplish the same
thing: they fire off a HTTP GET method.</p>

<p>
    If using <code>curl</code>, make sure it is installed on your target system.
    Ubuntu, for example, does not have curl installed out of the box.
</p>

{% include "front/snippets/bash.html" %}

<h3>Python</h3>
{% include "front/snippets/python.html" %}

<h3>Node</h3>
{% include "front/snippets/node.html" %}


<h3>PHP</h3>
{% include "front/snippets/php.html" %}

<h3>Browser</h3>
<p>
    healthchecks.io includes <code>Access-Control-Allow-Origin:*</code>
    CORS header in its ping responses, so cross-domain AJAX requests
    should work.
</p>
{% include "front/snippets/browser.html" %}

<h3>Email</h3>
<p>
    As an alternative to HTTP/HTTPS requests,
    you can "ping" this check by sending an
    email message to <a href="mailto:{{ check.email }}">{{ check.email }}</a>
</p>
<p>
    This is useful for end-to-end testing weekly email delivery.
</p>
<p>
    An example scenario: you have a cron job which runs weekly and
    sends weekly email reports to a list of e-mail addresses. You have already
    set up a check to get alerted when your cron job fails to run.
    But what you ultimately want to check is your emails <em>get sent and
    get delivered</em>.
</p>
<p>
    The solution: set up another check, and add its
    @hchk.io address to your list of recipient email addresses. Set its
    Period to 1 week. As long as your weekly email script runs correctly,
    the check will be regularly pinged and will stay up.
</p>


<h2>When Alerts Are Sent</h2>
<p>
    Each check has a configurable <strong>Period</strong> parameter, with the default value of one day.
    For periodic tasks, this is the expected time gap between two runs.
</p>
<p>
    Additionally, each check has a <strong>Grace</strong> parameter, with default value of one hour.
    You can use this parameter to account for run time variance of tasks.
    For example, if a backup task completes in 50 seconds one day, and
    completes in 60 seconds the following day, you might not want to get
    alerted because the backups are 10 seconds late.
</p>
<p>Each check can be in one of the following states:</p>

<table class="table">
    <tr>
        <td>
            <span class="glyphicon glyphicon-question-sign new"></span>
        </td>
        <td>
            <strong>New.</strong>
            A check that has been created, but has not received any pings yet.
        </td>
    </tr>
    <tr>
        <td>
            <span class="glyphicon glyphicon-ok-sign up"></span>
        </td>
        <td>
            <strong>Up.</strong>
            Time since last ping has not exceeded <strong>Period</strong>.
        </td>
    </tr>
    <tr>
        <td>
            <span class="glyphicon glyphicon-exclamation-sign grace"></span>
        </td>
        <td>
            <strong>Late.</strong>
            Time since last ping has exceeded <strong>Period</strong>,
            but has not yet exceeded <strong>Period</strong> + <strong>Grace</strong>.
        </td>
    </tr>
    <tr>
        <td>
            <span class="glyphicon glyphicon-exclamation-sign down"></span>
        </td>
        <td>
            <strong>Down.</strong>
            Time since last ping has exceeded <strong>Period</strong> + <strong>Grace</strong>.
            When check goes from "Late" to "Down", healthchecks.io
            sends you an alert.
        </td>
    </tr>
</table>

</div></div>
{% endblock %}