Zabbix Documentation 3.4

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manual:config:event_correlation

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5 Event correlation

Overview

While generally OK events close all problem events in Zabbix, there are cases when a more detailed approach is needed. For example, when monitoring log files you may want to discover certain problems in a log file and close them individually rather than all together.

This is the case with triggers that have Multiple Problem Event Generation enabled. Such triggers are normally used for log monitoring, trap processing, etc.

It is possible in Zabbix to relate problem events based on the event tags. Tags are used to extract values and create identification for problem events. Taking advantage of that, problems can also be closed individually based on matching tag.

In other words, the same trigger can create separate events identified by the event tag. Therefore problem events can be identified one-by-one and closed separately based on the identification by the event tag.

Correlation can be defined in:

  • trigger configuration - one trigger may be used to relate problems to their solution
  • globally - it is possible to relate problems to their solution from a different trigger/polling method using global correlation rules

How it works

In log monitoring you may encounter lines similar to these:

Line1: Application 1 stopped
Line2: Application 2 stopped
Line3: Application 1 was restarted
Line4: Application 2 was restarted

The idea of event correlation is to be able to match the problem event from Line1 to the resolution from Line3 and the problem event from Line2 to the resolution from Line4, and close these problems one by one:

Line1: Application 1 stopped
Line3: Application 1 was restarted #problem from Line 1 closed

Line2: Application 2 stopped
Line4: Application 2 was restarted #problem from Line 2 closed

To do this you need to tag these related events as, for example, “Application 1” and “Application 2”. That can be done by applying a regular expression to the log line to extract the tag value. Then, when events are created, they are tagged “Application 1” and “Application 2” respectively and problem can be matched to the resolution.

Configuration

To configure event correlation on trigger level:

  • select 'Problem event generation mode' as Multiple
  • select that 'OK event closes' All problems if tag values match
  • enter the name of the tag for event matching
  • configure the tags to extract tag values from log lines

If configured successfully you will be able to see problem events tagged by application and matched to their resolution in MonitoringProblems.

Because misconfiguration is possible, when similar event tags may be created for unrelated problems, please review the cases outlined below!
  • With two applications writing error and recovery messages to the same log file a user may decide to use two Application tags in the same trigger with different tag values by using separate regular expressions in the tag values to extract the names of, say, application A and application B from the {ITEM.VALUE} macro (e.g. when the message formats differ). However, this may not work as planned if there is no match to the regular expressions. Non-matching regexps will yield empty tag values and a single empty tag value in both problem and OK events is enough to correlate them. So a recovery message from application A may accidentally close an error message from application B.
  • Actual tags and tag values only become visible when a trigger fires. If the regular expression used is invalid, it is silently replaced with an *UNKNOWN* string. If the initial problem event with an *UNKNOWN* tag value is missed, there may appear subsequent OK events with the same *UNKNOWN* tag value that may close problem events which they shouldn't have closed.
  • If a user uses the {ITEM.VALUE} macro without macro functions as the tag value, the 255-character limitation applies. When log messages are long and the first 255 characters are non-specific, this may also result in similar event tags for unrelated problems.

Configuring global correlation

In a slightly different scenario, you may have different triggers for problem and resolution. For example, a log trigger may report application problems, while a polling trigger may report the application to be up and running.

Taking advantage of event tags you can tag the log trigger as Status: Down while tag the polling trigger as Status: Up. Then, in a global correlation rule you can relate these triggers and assign operations to this correlation such as close old events or close new events.

To configure event correlation rules globally:

  • go to ConfigurationEvent correlation
  • Click on Create correlation to the right (or on the correlation name to edit an existing rule)
  • Enter parameters of the correlation rule in the form

ParameterDescription
Name Unique correlation rule name.
Type of calculation The following options of calculating conditions are available:
And - all conditions must be met
Or - enough if one condition is met
And/Or - AND with different condition types and OR with the same condition type
Custom expression - a user-defined calculation formula for evaluating action conditions. It must include all conditions (represented as uppercase letters A, B, C, …) and may include spaces, tabs, brackets ( ), and (case sensitive), or (case sensitive).
Conditions List of conditions, selected fromthe New condition field.
New condition Select conditions upon which events are correlated and click on Add. The following conditions are available:
Old event tag - match new events to the specified old event tag
New event tag - match old events to the specified new event tag
New event host group - filter matched events to the specified new event host group(s)
Event tag pair - match events if the values of the specified tag pair match
Old event tag value - match new events to the specified old event tag value
New event tag value - match old events to the specified new event tag value
Description Correlation rule description.
Enabled If you mark this checkbox, the correlation rule will be enabled.
  • Select the operation of the correlation rule in the form

ParameterDescription
Operations List of operations, selected from the New operation field.
New operation Select operation to perform when event is correlated and click on Add. The following operations are available:
Close old events - close old events when a new event happens. Always add a condition based on the old event when using the Close old events operation or all existing problems could be closed.
Close new event - close the new event when it happens
Because misconfiguration is possible, when similar event tags may be created for unrelated problems, please review the cases outlined below!
  • Actual tags and tag values only become visible when a trigger fires. If the regular expression used is invalid, it is silently replaced with an *UNKNOWN* string. If the initial problem event with an *UNKNOWN* tag value is missed, there may appear subsequent OK events with the same *UNKNOWN* tag value that may close problem events which they shouldn't have closed.
  • If a user uses the {ITEM.VALUE} macro without macro functions as the tag value, the 255-character limitation applies. When log messages are long and the first 255 characters are non-specific, this may also result in similar event tags for unrelated problems.