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An introduction to Alerting
An introduction to Alerting

Discover how to get started with the setup and configuration of alerts with in our helpful guide.

Lee Smith avatar
Written by Lee Smith
Updated over a week ago

Alerting and Notifications

Proactive alerting is crucial to any organisation, whether it be critical production errors in your logs, server metrics exceeding expected thresholds or security alerting when someone is trying to gain unauthorised access to your system. 

With, your team can get notified and receive alerts with our built-in integrations that complement your existing workflow. Choose from many notification options, including Email and Slack. You can also receive webhooks into your applications to automatically restart a service or raise a PagerDuty alert to notify your team.

You can configure flexible and powerful alerting directly from your dashboard using your existing OpenSearch queries. Not only does this protect your organisation and ensure you stay compliant, but it helps everyone to sleep easy at night.

Rule Types

Several rule types with common monitoring paradigms are included with

  • “Match where there are X events in Y time” (frequency type)

  • “Match when the rate of events increases or decreases” (spike type)

  • “Match when there are less than X events in Y time” (flatline type)

  • “Match when a certain field matches a blacklist/whitelist” (blacklist and whitelist type)

  • “Match on any event matching a given filter” (any type)

  • “Match when a field has two different values within some time” (change type)

In addition to this basic usage, there are many other features that make alerts more useful:

  • Alerts link to OpenSearch Dashboards

  • Aggregate counts for arbitrary fields

  • Combine alerts into periodic reports

  • Separate alerts by using a unique key field

  • Intercept and enhance match data

# From example_rules/example_frequency.yaml
es_port: 14900
name: Example rule
type: frequency
index: logstash-*
num_events: 50
    hours: 4
- term:
    some_field: "some_value"
- "email"
- ""

Here is a repository with example alert YAML files that will help you create your own alert rules.

Frequently Asked Questions

My rule is not getting any hits?

If you write a rule and run it, but nothing happens or the query shows 0 hits and you have tested the rule to see how many documents match your filters in the last 2 hours, you should try removing the filter from your rule and try testing it again.  This will show you if the index is correct and you have at least some documents.  If you have a filter in OpenSearch and you would like to recreate it, you would probably need to use a query string so that your filter looks like this:

- query:
      query: "foo: bar AND baz: abc*"

If you received an error in your alert rule, it is likely that the YAML is not spaced correctly and the filter is not in the right format.  If you are using other types of filters, like term, a common problem is not realising that you need to use the analysed token. This is the default if you are using Logstash. For example:

- term:
    foo: "Test Document"

This will not match even if the original value for foo was exactly "Test Document". Instead you want to use foo.raw.

I got hits, why didn't I get an alert?

If you got logs that had X query hits, 0 matches, 0 alerts sent, it will depend on the type that you have used.  If you used type: any a match will occur for every hit.  If you used type: frequency then the num_events must occur within the timeframe for a match to occur.  Different rules apply for the different rule types.

es_port: 9200

name: Log frequency rule
type: frequency
index: logstash-*
is_enabled: false

  minutes: 1
  minutes: 1

num_events: 30
  seconds: 30

- "email"
- ""

If you see X matches, 0 alerts sent, this may have occurred for several reasons.  If you have set an aggregation, the alert will not be sent until after that time has been elapsed.  If you have gotten an alert for this same rule before then rule could have been silenced for a period of time.  The default time for alerts is set to fire every one minute between alerts.  If the rule is silenced you would see Ignoring match for silenced rule in the logs.

Why did I only get one alert when I expected to get several?

There is a setting called realert  which is the minimum time between two alerts for the same rule.  Any alert that occurs within this time will simply be dropped.  The default value is set to one minute.  So if you want to receive an alert for every match, even if they occur right after each other you can use: 

  minutes: 0

You can also set it higher as well.

How can I prevent duplicate alerts?

By setting realert, you will prevent the same rule from alerting twice in an amount of time.

  days: 1

You can also prevent duplicates based on a certain field by using query_key. For example, to prevent multiple alerts for the same user, you might use

  hours: 8
query_key: user

How can I make the alert come at a certain time?

The aggregation feature will take every alert that has occurred over a period of time and send them together in one alert. You can use cron style syntax to send all alerts that have occurred since the last one by using

  schedule: '2 4 * * mon,fri'

I'm not using @timestamp, what do I do?

You can use timestamp_field to change which field ElastAlert will use as the timestamp. You can use timestamp_type to change it between ISO8601 and Unix timestamps. You must have some kind of timestamp for ElastAlert to work. If your events are not in real-time, you can use query_delay and buffer_time to adjust when ElastAlert will look for documents.

If you have a second timestamp field other than @timestamp, you can use that instead by setting:

timestamp_field: log-time

What's next?

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