Pass date or cron schedule from cloud watch events to step function input

Question

Is there a way I can pass a date or a cron schedule as an input to my state function - which is getting called by a cloud watch event? The cloud watch event runs on a cron schedule and I would like to pass that dynamically on a daily basis to the step function

For example:

This gives some static input, but I want to give each day's date as input

resource "aws_cloudwatch_event_target" "target" {

rule = aws_cloudwatch_event_rule.samplerule.id
arn = aws_sfn_state_machine.samplemachine.id
role_arn = aws_iam_role.iam_for_sfn.arn
input = <<EOF
{
  "operand1": "3",
  "operand2": "5",
  "operator": "add"
}
EOF
}

Answer 1

The input to your Lambda function from a Scheduled Event looks something like this:

{
 "id": "53dc4d37-cffa-4f76-80c9-8b7d4a4d2eaa",
 "detail-type": "Scheduled Event",
 "source": "aws.events",
 "account": "123456789012",
 "time": "2019-10-08T16:53:06Z",
 "region": "us-east-1",
 "resources": [ "arn:aws:events:us-east-1:123456789012:rule/MyScheduledRule" ],
 "detail": {}
}

Using your choice of programming language, you can extract the time value and convert it from a string to a date resource/object (depending on your language). From that time, you can get the data components you are looking for.

IMPORTANT: All scheduled events use UTC time zone and the minimum precision for schedules is 1 minute: https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/ScheduledEvents.html

Answer 2

An alternative solution could be to use the global access to the context object , as explained here to get the execution start time of the step functions state machine.

So you can send it through your different states of your state machine like this:

"mystep1": {
  "Type": "task",
  "Parameters": {
    "StartTime.$": "$$.Execution.StartTime"
 }
...
}

Make sure to use the double $ to tell Cloudformation that you're using the global access to the context object.