Schedule Expressions for Rules – Amazon CloudWatch Events
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Schedule Expressions for Rules
Note
Amazon EventBridge is the preferred way to manage your events. CloudWatch Events and EventBridge are the same
underlying service and API, but EventBridge provides more features. Changes you make
in either CloudWatch or EventBridge will appear in each console. For more information, see Amazon EventBridge.
You can create rules that self-trigger on an automated schedule in CloudWatch Events using cron or
rate expressions. All scheduled events use UTC time zone and the minimum precision for
schedules is 1 minute.
CloudWatch Events supports cron expressions and rate expressions. Rate expressions are simpler to define but don’t offer
the fine-grained schedule control that cron expressions support. For example, with a cron expression, you can define a
rule that triggers at a specified time on a certain day of each week or month. In contrast, rate expressions trigger a rule at
a regular rate, such as once every hour or once every day.
Note
CloudWatch Events does not provide second-level precision in schedule expressions. The finest
resolution using a cron expression is a minute. Due to the distributed nature of the CloudWatch Events
and the target services, the delay between the time the scheduled rule is triggered and the
time the target service honors the execution of the target resource might be several
seconds. Your scheduled rule is triggered within that minute, but not on the precise 0th
second.
Cron Expressions
Cron expressions have six required fields, which are separated by white space.
Syntax
cron(fields)
Field
Values
Wildcards
Minutes
0-59
, – * /
Hours
0-23
, – * /
Day-of-month
1-31
, – * ? / L W
Month
1-12 or JAN-DEC
, – * /
Day-of-week
1-7 or SUN-SAT
, – * ? L #
Year
1970-2199
, – * /
Wildcards
-
The , (comma) wildcard includes additional values. In the
Month field, JAN,FEB,MAR would include January, February, and March. -
The – (dash) wildcard specifies ranges. In the Day field,
1-15 would include days 1 through 15 of the specified month. -
The * (asterisk) wildcard includes all values in the field.
In the Hours field, * would include every hour. You cannot use *
in both the Day-of-month and Day-of-week fields. If you use it in one, you must use ?
in the other. -
The / (forward slash) wildcard specifies increments. In the
Minutes field, you could enter 1/10 to specify every tenth minute, starting from the
first minute of the hour (for example, the 11th, 21st, and 31st minute, and so
on). -
The ? (question mark) wildcard specifies one or another. In
the Day-of-month field you could enter 7 and if you didn’t care
what day of the week the 7th was, you could enter ? in the
Day-of-week field. -
The L wildcard in the Day-of-month or Day-of-week fields
specifies the last day of the month or week. -
The
W
wildcard in the Day-of-month field specifies a weekday.
In the Day-of-month field,3W
specifies the weekday closest to the third day of the
month. -
The # wildcard in the Day-of-week field specifies a certain instance
of the specified day of the week within a month. For example, 3#2 would be the second Tuesday of the month: the
3 refers to Tuesday because it is the third day of each week, and the 2 refers to the second day of that type within
the month.Note
If you use a ‘#’ character, you can define only one expression in the day-of-week field. For example,
"3#1,6#3"
is not valid
because it is interpreted as two expressions.
Restrictions
-
You can’t specify the Day-of-month and Day-of-week fields in the same cron
expression. If you specify a value (or a *) in one of the fields, you must use a
? (question mark) in the other. -
Cron expressions that lead to rates faster than 1 minute are not supported.
Examples
You can use the following sample cron strings when creating a rule with
schedule.
Minutes
Hours
Day of month
Month
Day of week
Year
Meaning
0
10
*
*
?
*
Run at 10:00 am (UTC) every day
15
12
*
*
?
*
Run at 12:15 pm (UTC) every day
0
18
?
*
MON-FRI
*
Run at 6:00 pm (UTC) every Monday through Friday
0
8
1
*
?
*
Run at 8:00 am (UTC) every 1st day of the month
0/15
*
*
*
?
*
Run every 15 minutes
0/10
*
?
*
MON-FRI
*
Run every 10 minutes Monday through Friday
0/5
8-17
?
*
MON-FRI
*
Run every 5 minutes Monday through Friday between 8:00 am and 5:55
pm (UTC)
The following examples show how to use Cron expressions with the AWS CLI
put-rule command. The first example creates a rule that is triggered every day at 12:00pm UTC.
aws events put-rule --schedule-expression "cron(0 12 * * ? *)" --name MyRule1
The next example creates a rule that is triggered every day, at 5 and 35 minutes past 2:00pm UTC.
aws events put-rule --schedule-expression "cron(5,35 14 * * ? *)" --name MyRule2
The next example creates a rule that is triggered at 10:15am UTC on the last Friday of each month during the years 2002 to 2005.
aws events put-rule --schedule-expression "cron(15 10 ? * 6L 2002-2005)" --name MyRule3
Rate Expressions
A rate expression starts when you create the scheduled event rule, and then runs on its defined schedule.
Rate expressions have two required fields. Fields are separated by white space.
Syntax
rate(value unit)
-
value
-
A positive number.
-
unit
-
The unit of time. Different units are required for values of 1, such as
minute
,
and values over 1, such asminutes
.Valid values: minute | minutes | hour | hours | day | days
Restrictions
If the value is equal to 1, then the unit must be singular. Similarly, for values
greater than 1, the unit must be plural. For example, rate(1 hours) and rate(5 hour)
are not valid, but rate(1 hour) and rate(5 hours) are valid.
Examples
The following examples show how to use rate expressions with the AWS CLI
put-rule command. The first example triggers the rule every minute, the
second example triggers it every 5 minutes,
the third triggers it once an hour, and the final example triggers it once a day.
aws events put-rule --schedule-expression "rate(1 minute)" --name MyRule2
aws events put-rule --schedule-expression "rate(5 minutes)" --name MyRule3
aws events put-rule --schedule-expression "rate(1 hour)" --name MyRule4
aws events put-rule --schedule-expression "rate(1 day)" --name MyRule5