CloudMonitor:Alert rule expressions

Elements

CloudMonitor calculates the aggregate data of metrics or a metric of an instance based on the alert rule expression that you configure. If the monitoring data meets the expression, an alert is triggered. An alert rule expression consists of metric names, metric members, operators, functions, and monitoring data, for example, @cpu_total[60].$instanceId != 'i-2ze3jvsy7620giru****' && @cpu_total[60].$Average > 60.

• Metric names

  For more information about the metrics of different cloud services, see Appendix 1: Metrics.

  The alert rule expression for a metric is in the @Metric name[Aggregation period] format. For example, to monitor an Elastic Compute Service (ECS) instance based on the CPUUtilization metric, you can set the alert rule expression to @CPUUtilization[60].

  Note

  • The aggregation period of metrics for ECS is displayed in the Min Periods column of the table on the Metric List page for ECS. To view the aggregation period of metrics for another cloud service, select the cloud service from the drop-down list.
  • A metric name must conform to the regular expression [a-zA-Z][_a-zA-Z0-9]*. If a metric name does not conform to the regular expression, use the @(Metric name)[Aggregation period] format, for example, @('vm.DiskIORead')[60].

  In an alert rule expression, metric names must be used in conjunction with metric members to specify the range of monitoring data.

• Metric members
  Metric members are used to specify the range of monitoring data for the related metrics. A metric member must start with a dollar sign ($). You must specify the alert rule expression in the @Metric name[Aggregation period].$Metric member format. For example, the statistical methods for the CPUUtilization metric of ECS are Average, Minimum, and Maximum. The alert rule expression for the average value of the metric is @CPUUtilization[60].$Average. The dimensions for the CPUUtilization metric of ECS are userId and instanceId. The alert rule expression for the CPUUtilization metric of a specified instance is @CPUUtilization[60].$instanceId.

  Note The members of metrics for ECS are displayed in the Dimensions and Statistics column of the table on the Metric List page for ECS. To view the members of metrics for another cloud service, select the cloud service from the drop-down list.
• Operators
  Operators are used to calculate whether the monitoring data meets the alert condition.

  • Basic operators

    Category	Operator and description
    Mathematical operators	+: addition -: subtraction *: multiplication /: division %: modulo **: exponentiation
    Comparison operators	==: equal to !=: not equal to >: greater than >=: greater than or equal to <: less than <=: less than or equal to
    Logical operators	&& or and: AND || or or: OR ! or not: NOT

    Example: $Average > 50 && $instanceId != 'i-not-exist'.

    Note If the values on the two sides of a mathematical operator or a comparison operator are not of the same type, a string is converted to a number, for example, '123' + 321 == 123 + '321' == 444.
  • String operators

    String operator	Description	Example
    matches	Matches a regular expression. The logical operator NOT and the matches operator are used to determine whether a string matches a regular expression.	!("hello" matches "^fo.+") Note The ! operator has higher priority than the matches operator. Therefore, you must enclose the regular expression in parentheses ().
    contains	Contains a string.	'abcdef' contains 'cde'
    startsWith	Checks whether a string starts with a specified prefix.	'abcdef' startsWith 'abc'
    endsWith	Checks whether a string ends with a specified suffix.	'abcdef' endsWith 'def'

  • Membership operators

    Membership operator	Description	Example
    in	Contains.	userld in [120886317861****,425876] The value of userld is 120886317861**** or 20654616023382****. "foo"in{'foo':1,'bar':2} The value of foo is foo or bar.
    not in	Does not contain.	userld not in [120886317861****,425876] The value of userld is not 120886317861**** or 20654616023382****. "foo"in{'foo1':1,'bar':2} The value of foo is not foo1 or bar.

  • Ternary operators

    ?:: The operator has the same effect as the ternary operators in C and Java languages, for example, @CPUUtilization[60].$Average > 30? "ok": "lower".

• Data operations
  • Data types

    Data type	Description	Example
    string	A string enclosed in single quotation marks or double quotation marks.	"hello", 'hello'
    number	A numeric value. The value can be an integer or a floating-point number. Note If the value is an integer, you can use underscores (_) as separators to improve readability and facilitate management.	103, 2.5, .5, 2e+6 1_000_000
    array	An array.	[1, 2, 3]
    map or dict	A dictionary.	{"foo":"bar"}
    bool	A Boolean value.	true or false
    nil	An empty value.	nil

  • Built-in functions

    Built-in function	Description
    len(array|map|string)	Returns the length of an array, map, or string.
    now()	Returns a UTC timestamp in milliseconds.
    abs(number)	Returns the absolute value (a floating-point number).
    rand()	Returns a floating-point number between [0, 1).
    rand(N)	Returns a floating-point number between [0, N).
    toLower(string)	Converts a string to lowercase.
    toUpper(string)	Converts a string to uppercase.

  • Comparison
    Note

    • Example of a metric: @cpu_total[60].
    • An aggregation method is a string. Example: '$Average'.
    • The comparison result is a Boolean value. If the metric value of the current period is greater than the metric value of the previous period, the comparison result is true. If the metric value of the current period is less than the metric value of the previous period, the comparison result is false.

    Function	Description
    CompareLastPeriod(metric, aggregation method, comparison result)	Obtains the data compared with the previous period, for example, CompareLastPeriod(@cpu_total[60], '$Average', true). If the average value of cpu_total in the current period is 20% and the average value of cpu_total in the previous period is 15%. the returned value of this function depends on the comparison result. If the comparison result is true, this function returns (20 - 15) × 100/20. If the comparison result is false, this function returns (15 - 20) × 100/20.
    CompareLastHour(metric, aggregation method, comparison result)	Obtains the data compared with the previous hour. CompareLastHour(@cpu_total[60], '$Average', true) > 10: If the average value of cpu_total increases by 10% compared with the previous hour, an alert is triggered.
    CompareYesterday(metric, aggregation method, comparison result)	Obtains the data compared with yesterday. CompareYesterday(@cpu_total[60], '$Average', true) > 10: If the average value of cpu_total increases by 10% compared with yesterday, an alert is triggered.
    CompareLastWeek(metric, aggregation method, comparison result)	Obtains the data compared with the previous week. CompareLastWeek(@cpu_total[60], '$Average', true) > 10: If the average value of cpu_total increases by 10% compared with the previous week, an alert is triggered.
    ComparePast(metric, aggregation method, comparison result, seconds)	Obtains the data compared with the specified number of seconds prior to the current time. The preceding four functions are simplified forms of this function. CompareLastHour(@cpu_total[60], '$Average', true) is equivalent to ComparePast(@cpu_total[60], '$Average', true, 3600). CompareYesterday(@cpu_total[60], '$Average', true) is equivalent to ComparePast(@cpu_total[60], '$Average', true, 24*60*60). CompareLastWeek(@cpu_total[60], '$Average', true) is equivalent to ComparePast(@cpu_total[60], '$Average', true, 7*24*60*60).

Scenarios