AWS EventBridge cron with Cron Studio
This opens cron(0 8 ? * MON-FRI *): 08:00 UTC on weekdays. It shows the explanation and next runs, and gives you the matching aws_cloudwatch_event_rule for Terraform.
- Check the six fields: minute, hour, day of month, month, day of week, year.
- Keep ? in either day-of-month or day-of-week, never * in both.
- Read the next runs in UTC; classic EventBridge rules always run in UTC.
- Copy the Terraform resource and set the rule target.
What to know
AWS cron has six fields, with a mandatory year at the end: cron(minutes hours day-of-month month day-of-week year). One of the two day fields must be ?. Weekdays are 1 to 7 starting at Sunday, or SUN to SAT. Writing cron(0 8 * * 1-5 *) fails because both day fields are set.
EventBridge rules always run in UTC. EventBridge Scheduler, the newer service, lets you choose a time zone, so a 9 AM schedule can follow daylight saving. The minimum granularity is one minute, and rate(5 minutes) is simpler than a cron expression when you just need a fixed interval.
The Terraform tab shows the schedule_expression string ready to paste into aws_cloudwatch_event_rule. Remember that the rule only decides when something fires: the target (a Lambda, a Step Functions state machine or an ECS task) and its permissions are configured separately.
Updated · Cosmovex
Questions
What is the AWS cron expression for every day at 8 AM?
cron(0 8 * * ? *): minute 0, hour 8 (UTC), every day of the month, every month, no specific weekday, every year.
Why does EventBridge reject my cron expression?
Most often both day fields contain a value. One of day-of-month and day-of-week must be ?. Another common cause is five fields instead of six.
Is AWS cron in UTC?
Classic EventBridge and CloudWatch rules use UTC. EventBridge Scheduler supports a time zone per schedule.
Can EventBridge run every 30 seconds?
No. The smallest cron or rate interval is one minute.
The free plan covers everything on this page. Cron Studio Pro ($19, paid once) is described on the Cron Studio page.
