apache--hertzbeat/home/docs/help/alert_threshold_expr.md

id, title, sidebar_label

id	title	sidebar_label
alert_threshold_expr	Threshold Trigger Expression	Threshold Trigger Expression

When configuring threshold alerts, it is necessary to set up threshold trigger expressions. The system calculates whether to trigger an alert based on the expression and the monitored metric values. Here, we provide a detailed explanation of expression usage.

Supported Operators in Expressions

Operator (Visual Configuration)	Operator (Expression Configuration)	Supported Types	Description
Equals	equals(str1,str2)	String	Check if strings are equal
Not Equals	!equals(str1,str2)	String	Check if strings are not equal
Contains	contains(str1,str2)	String	Check if string contains
Not Contains	!contains(str1,str2)	String	Check if string does not contain
Matches	matches(str1,str2)	String	Check if string matches regex
Not Matches	!matches(str1,str2)	String	Check if string does not match regex
Exists	exists(obj)	String, Numeric, Time	Check if value exists
Not Exists	!exists(obj)	String, Numeric, Time	Check if value does not exist
Greater than	obj1 > obj2	Numeric, Time	Check if value is greater than
Less than	obj1 < obj2	Numeric, Time	Check if value is less than
Greater than or Equal to	obj1 >= obj2	Numeric, Time	Check if value is greater than or equal to
Less than or Equal to	obj1 <= obj2	Numeric, Time	Check if value is less than or equal to
Not Equal to	obj1 != obj2	Numeric, Time	Check if values are not equal
Equal to	obj1 == obj2	Numeric, Time	Check if values are equal

Expression Function Library List

Supported Function Library	Description
condition ? trueExpression : falseExpression	Ternary operator
toDouble(str)	Convert string to Double type
toBoolean(str)	Convert string to Boolean type
toInteger(str)	Convert string to Integer type
array[n]	Retrieve the nth element of an array
*	Multiplication
/	Division
%	Modulo
( and )	Parentheses for controlling the order of operations in logical or mathematical expressions
+	Addition
-	Subtraction
&&	Logical AND operator
||	Logical OR operator

Supported Environment Variables

Environment variables refer to variables supported by metric values, used in expressions. During threshold calculation and judgment, these variables will be replaced with actual values.

Non-fixed Environment Variables: These variables change dynamically based on the selected monitoring metric. For example, if we choose response time metric for website monitoring, the environment variable would be responseTime - this represents response time variable. If we want to set an alert trigger for response time greater than 400 for website monitoring, the expression would be responseTime>400.

Fixed Environment Variables (Less commonly used): instance: instance value This variable is mainly used for calculations involving multiple instances. For instance, if we collect usage metrics for C drive and D drive (usage being a non-fixed environment variable), and we only want to set an alert for usage greater than 80 for the C drive, the expression would be equals(instance,"c")&&usage>80.

Expression Configuration Examples

1. Website Monitoring -> Alert when response time is greater than or equal to 400ms responseTime>=400
2. API Monitoring -> Alert when response time is greater than 3000ms responseTime>3000
3. Overall Monitoring -> Alert when response time for URL (instance) path 'https://baidu.com' is greater than 200ms equals(instance,"https://baidu.com")&&responseTime>200
4. MYSQL Monitoring -> Alert when 'threads_running' metric under 'status' exceeds 7 threads_running>7

If you encounter any issues, feel free to discuss and provide feedback through our community group or ISSUE tracker!