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Run an AWS EventBridge schedule every 5 seconds

AWS EventBridge has no exact expression for “Every 5 seconds”. Here is why, a workaround, and the platforms that can do it. AWS EventBridge Scheduler takes cron() with six fields, minutes to year, in the time zone you set (UTC by default).

Why AWS EventBridge can’t do this exactly

Defined on Quartz as */5 * * * * ? · “Every 5 seconds”

  • second: AWS EventBridge has no seconds field, so it cannot run at seconds other than 0.

    WorkaroundRun every minute and repeat inside the job with sleep, or use a scheduler that has seconds (Spring, Quartz, a systemd timer).

AWS EventBridge gotchas

Six fields inside cron()Minutes, hours, day of month, month, day of week, year. There is no seconds field.
One day field must be ?If you set day of month, write ? for day of week, and the other way round. Setting both is an error.
Sunday is 1Day of week runs 1-7 from SUN, so 2-6 is Monday to Friday.
No step in day of weekDay of week takes lists, ranges, L and one #, but not /. List the days instead.

FAQ

What is the AWS EventBridge cron expression for “Every 5 seconds”?

There is none that matches exactly. AWS EventBridge has no seconds field, so it cannot run at seconds other than 0.

Which time zone does a AWS EventBridge schedule use?

EventBridge Scheduler takes --schedule-expression-timezone with an IANA name and defaults to UTC. Older EventBridge rules only run in UTC.

What is the difference between rate() and cron()?

rate(5 minutes) runs at a fixed interval from when the schedule starts; cron() runs at clock times. Use cron() when the minute matters.

EventBridge Scheduler or EventBridge rules?

AWS recommends EventBridge Scheduler for new schedules: it supports time zones and one-time schedules. Rules only run in UTC.