Amazon EventBridge Scheduler and DST Support

I needed to update an AWS CloudWatch event rule in a SAM project which I have to do twice a year because of DST. The rule is to execute a Step Function every work day at 3 particular times. Because of DST changes during the year I had to adjust the start time by adding or subtracting an hour.

I decided to instead use the Amazon EventBridge Scheduler which supports DST. #serverlessland has an example of exactly what I needed at https://serverlessland.com/patterns/eventbridge-schedule-to-lambda

The one change that I had to make to the example template was the cron schedule and timezone that I wanted it to use.

The result looks like this:

  TestScheduler:
    Type: AWS::Scheduler::Schedule
    Properties: 
      Description: >
        Example of using the EventBridge Scheduler with local timezone support
        provided by the ScheduleExpressionTimezone attribute.
      FlexibleTimeWindow: 
        Mode: 'OFF'
      Name: 'TestEventBridgeScheduler'
      # every workday at 4:00, 4:15, 4:30pm ET
      ScheduleExpression: 'cron(0,15,30 16 ? * MON-FRI *)'
      ScheduleExpressionTimezone: 'America/New_York'
      State: 'ENABLED'
      Target: 
        Arn: !GetAtt ScheduledLambdaFunction.Arn
        RoleArn: !GetAtt MyFirstScheduleRole.Arn

In my SAM project I will switch this to my Step Function and it will now work correctly for the entire year without me having to make my twice a year change.

Note that you also need to allow the scheduler principal to perform an assumeRole for this if you already have a role defined for your Step Function.

      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service:
                - scheduler.amazonaws.com
            Action:
              - sts:AssumeRole

https://serverlessland.com/ is always an excellent place to find examples, patterns, and tips in general.

The EventBridge Scheduler documentation is at https://docs.aws.amazon.com/eventbridge/latest/userguide/scheduled-events.html

AWS announcements can be found at https://aws.amazon.com/new