AWS CloudFormation for StepFunctions. Passing the DefinitionString as parameter

Question

I am trying to create a CloudFormation for StepFunctions. I would like to pass the DefinitionString as a parameter. The json string is pretty big . The max cap is 4096 bytes. How do i handle to such cases where parameter is more than the upper cap . Sample template is given below

{
   "AWSTemplateFormatVersion" : "2010-09-09",
   "Description" : "An example template for a Step Functions state machine.",
   "Resources" : {
      "MyStateMachine" : {
         "Type" : "AWS::StepFunctions::StateMachine",
         "Properties" : {
            "StateMachineName" : "HelloWorld-StateMachine",
            "DefinitionString" : "{\"StartAt\": \"HelloWorld\", \"States\": {\"HelloWorld\": {\"Type\": \"Task\", \"Resource\": \"arn:aws:lambda:us-east-1:111122223333:function:HelloFunction\", \"End\": true}}}",
            "RoleArn" : "arn:aws:iam::111122223333:role/service-role/StatesExecutionRole-us-east-1"
         }
      }
   }
}

May I ask you why you want to pass the DefinitionString as a parameter? If you parametrize nearly everything it's indicator that you are doing/understand something wrong. The main benefit of AWS CloudFormation that you got your Infrastructure as Code — MaiKaY
– MaiKaY, Commented Jul 18, 2018 at 7:34
How do i version control the Definition string json . I would like to keep the definition json separately . If there is any change to definition , i would re run my CI set up and update the stack with the new json . Also keeping it separately gives me more readability . Pls let me know your thoughts . @MaiKaY — Balaji V
– Balaji V, Commented Jul 18, 2018 at 7:44
And what is about just putting the DefinitionString into your CloudFormation template? As soon as you want to change something, do it, commit/push it to your version control (e.g. git) and update your stack manually or automatically. I still don't see the reason putting it as a parameter... — MaiKaY
– MaiKaY, Commented Jul 18, 2018 at 9:34
Dont i have to stringify it and put it in the template . Wont it be easier to read the json format of it and make changes . Else ill have to take the string , un escape it and correct it . I still think it ll be too cluttered . let me know your thoughts — Balaji V
– Balaji V, Commented Jul 18, 2018 at 14:01
@BalajiV If the only issue is escaping JSON then you can just use YAML CloudFormation template with string literals. Example: stackoverflow.com/questions/49373039/… (look at State Machine definition) — Marcin Sucharski
– Marcin Sucharski, Commented Aug 23, 2018 at 18:29

Mhairi McNeill · Accepted Answer · 2024-03-08 15:22:48Z

1

If anyone else is struggling with the 4069 byte max, then you can upload the Step Function definition to a s3 bucket and use the DefinitionS3Location parameter instead.

See: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-stepfunctions-statemachine.html

answered Mar 8, 2024 at 15:22

Mhairi McNeill

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