How to create recursion in AWS Step Functions-CodePudding

How to create step which will be repeated if lambda function will return "failed" status.

job2 = job1.next(Choice(self, "Check status.").when(Condition.number_equals("$.statusCode", 200), job3).otherwise(job2))

CodePudding user response：

You cannot internally to just Step Function... or more accurately, there may be a way but if you do go down that rather complex and overly complicated path you are going to set yourself to be charged 1000s of dollars as a failed lambda causes the system to rerun continuously and charging you every time.

You can do something with a Dead Letter Queue or a Catch in your Step Function definition to add an even too an SQS queue and have that fire every so often to re start failed jobs. But again. Be careful. It would be very easy to end up charging yourself/your company thousand of dollars very easily

CodePudding user response：

The Choice state should have 3 branches:

if job1 succeeded, go to job2
if job1 failed AND a retry count has not been reached, loop incrementTask -> job1
otherwise go to the Fail state

checkStatus = (
    sfn.Choice(self, "CheckStatus")
    .when(sfn.Condition.number_equals("$.job1.statusCode", 200), job2)
    .when(
        sfn.Condition.and_(
            sfn.Condition.not_(sfn.Condition.number_equals("$.job1.statusCode", 200)),
            sfn.Condition.or_(
                sfn.Condition.is_not_present("$.retryCount"),
                sfn.Condition.number_less_than("$.retryCount", 3),
            ),
        ),
        incrementTask.next(job1),
    )
    .otherwise(fail)
)

Add a Lambda Task that increments the retry count before looping back to job1. Make sure to set a result_path on job1 so that it does not overwrite the retryCount.

# incrementTask handler
def handler(event, context):
      event["retryCount"] = event.get("retryCount", 0)   1
      return event

The state machine will look like this:

state machine