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Alert Rules Engine: Variable Expansion

The Rules Engine can pull the content of an alert field into the rule, thus allowing users to dynamically update any annotation or transformation with data from the alert. This can be done using the payload field with the syntax: ${{field_name}}. Or it can be done by using a regular expression (RegEx) capture group with the syntax: ${{\n}} where n is the number of the capture group.

Variable Expansion Via Payload Field

  • Pull the name of the affected host from the alert and add it into the URL link for your wiki documentation. (The field in the alert containing this information is host_name)


  • Turn an image link provided by the monitoring tool into an annotation.


  • Combine multiple fields into the state_message so your users get more information in their notifications, without losing the original information in that field.  (Assuming the field you want to include is error_message)


Variable Expansion Via RegEx Capture Group

Regular expression capture groups are defined within parenthesis. You can use these capture groups for variable expansion the same way as payload fields. The only difference is the need to reference the value with the capture group number as seen below.

“([^\n]+)” captures one or more characters that are not a new line character.

Updated on August 15, 2019

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