healthchecks_healthchecks/templates/docs/configuring_checks.md

# Configuring Checks

In SITE_NAME, a **Check** represents a single service you want to
monitor. For example, when monitoring cron jobs, you would create a separate check for
each cron job you wish to monitor. SITE_NAME pricing plans are structured primarily
around how many checks you can have in your account. You can create checks
in the SITE_NAME web interface or via [Management API](../api/).

## Name, Tags, Description

Describe each check using an optional name, slug, tags, and description fields.

![Editing name, tags and description](IMG_URL/edit_name.png)

* **Name**: names are optional, but setting them is a good idea.
Good naming becomes especially important as you add more checks to the
account. SITE_NAME will display check names in the web interface, email reports,
and notifications.
* **Slug**: URL-friendly identifier used in [slug-based ping URLs](../http_api/#success-slug)
(an alternative to the default UUID-based ping URLs). The slug should only contain the
following characters: `a-z`, `0-9`, hyphens, and underscores. If you don't plan to use
slug-based ping URLs, you can leave the slug field empty.
* **Tags**: a space-separated list of optional labels. Use tags to organize and group
checks within a project. You can tag checks by the environment
(`prod`, `staging`, `dev`, etc.), by role (`www`, `db`, `worker`, etc.), or by using
any other system.
* **Description**: a free-form text field with any related information for your team
or your future self. Describe the cron job's role, who set it up, what to do in
case of failures, and where to look for additional information.

## Simple Schedules

SITE_NAME supports three types of schedules: **Simple**, **Cron**, and **OnCalendar**.
Use Simple schedules for monitoring processes that you expect to run at relatively
regular intervals: once an hour, once a day, once a week, etc.

![Editing the period and grace time](IMG_URL/edit_simple_schedule.png)

For the simple schedules, you can configure two parameters, Period and Grace Time.

* **Period** is the expected time between pings.
* **Grace Time** is the additional time to wait before sending an alert when a check
is late. Use this parameter to account for minor, expected deviations in job
execution times.

Note: if you use the "start" signal to [measure job run times](../measuring_script_run_time/),
then Grace Time also specifies the maximum allowed time gap between "start" and
"success" signals. Whenever SITE_NAME receives a "start" signal, it expects a subsequent 
"success" signal within Grace Time. If the success signal does not arrive within the 
configured Grace Time, SITE_NAME will mark the check as failed and send out alerts.

## Cron Schedules

Use "Cron" for monitoring cron jobs and other processes with more complex schedules.
This monitoring mode ensures that jobs run **at the correct time** and not just at
the correct time intervals.

See [Cron syntax cheatsheet](../cron/) for cron expression syntax examples.
See [crontab(5) man page](https://www.man7.org/linux/man-pages/man5/crontab.5.html)
for complete cron syntax reference.

![Editing cron schedule](IMG_URL/edit_cron_schedule.png)

You will need to specify Cron Expression, Server's Time Zone, and Grace Time.

* **Cron Expression** is the cron expression you specified in the crontab.
* **Server's Time Zone** is the timezone of your server. The cron daemon typically uses
the system's local time. If the machine does not use the UTC timezone, specify its
timezone here.
* **Grace Time**, same as for simple schedules, is how long to wait before sending an
alert for a late check.

## OnCalendar Schedules

Use "OnCalendar" schedules to monitor systemd timers that use `OnCalendar=` schedules.
Same as with systemd timers, you can specify more than one `OnCalendar` expression,
and SITE_NAME will expect a ping whenever any schedule matches.

See [systemd.time(7) man page](https://www.man7.org/linux/man-pages/man7/systemd.time.7.html#CALENDAR_EVENTS)
for complete OnCalendar syntax reference.

![Editing cron schedule](IMG_URL/edit_oncalendar_schedule.png)

## Filtering Rules

In the "Filtering Rules" dialog, you can control several advanced aspects of
how SITE_NAME handles incoming pings for a particular check.

![Setting filtering rules](IMG_URL/filtering_rules.png)

* **Allowed request methods for HTTP requests**. You can require the ping
requests to use HTTP POST. Use the "Only POST" option if you run into issues of
preview bots hitting the ping URLs when you send them in email or post them in chat.
* **Filter by keywords in the Subject line**. When pinging [via email](../email/),
you can instruct SITE_NAME to look for specific keywords in the subject line. If the
subject line contains any of the keywords listed in **Start Keywords**,
**Success Keywords**, or **Failure Keywords**, SITE_NAME will classify the email as
a start, a success, or a failure signal, respectively. Keyword matching is case-sensitive.
SITE_NAME will first checks for the presence of **Failure** keywords, then **Success**
keywords, and then **Start** keywords. If filtering is enabled but no keywords
match, SITE_NAME will **ignore** the email message. The email will show in the event log
with an "Ignored" badge.<br>The keyword filtering feature is useful if, for example,
your backup  software sends an email after each backup run, but with a different subject
line depending on success or failure.
* **Filter by keywords in the message body**. Same as the previous option, but
looks for the keywords in the email message body. SITE_NAME checks for keywords both in
the plain text and the HTML parts of email messages.
* **Pinging a Paused Check**. Normally, when you ping a paused check, it leaves the
paused state and goes into the "up" state (or the "down" state
in case of [a failure signal](../signaling_failures/)).
You can change this behavior by selecting the "Ignore the ping, stay in
the paused state" option. With this option selected, the paused state becomes "sticky":
SITE_NAME will ignore all incoming pings until you explicitly *resume* the check.