How to pass the Arn of a Step function to another function in a CloudFormation stack? - aws-lambda

Question

I created a step function in a CloudFormation stack, and I need to call that function from another function in the stack once it's deployed. I have no idea how to do that, and I'm getting circular dependencies.
Basically I'm trying to pass an environment variable to the function that's the ARN of the step function.
Here's the CloudFormation code :
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
reports stack
Globals:
Function:
Timeout: 120
MemorySize: 2048
Runtime: python3.9
Environment:
Variables:
STEP_FUNCTION: !GetAtt Research.Arn ### =====> how do i do that ?
Parameters:
ProjectName:
Description: Name of the Project
Type: String
Default: Project
Resources:
MyApi:
Type: AWS::Serverless::Api
Properties:
StageName: Prod
TracingEnabled: true
Cors:
AllowMethods: "'DELETE,GET,HEAD,OPTIONS,POST,PUT'"
AllowHeaders: "'Content-Type,X-Amz-Date,Authorization,X-Api-Key,X-Amz-Security-Token'"
AllowOrigin: "'*'"
List:
DependsOn: VideoResearch
Type: AWS::Serverless::Function
Properties:
CodeUri: functions/
Handler: get.get
Events:
List:
Type: Api
Properties:
RestApiId: !Ref MyApi
Path: /reports
Method: GET
Policies:
(...)
################ STEP FUNCTION ################
Research:
Type: AWS::Serverless::Function
Properties:
CodeUri: functions/
Handler: runResearch.research
Policies:
(...)
StepFunctionToHandleResearchRole:
Type: "AWS::IAM::Role"
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
- Effect: "Allow"
Principal:
Service:
- !Sub states.${AWS::Region}.amazonaws.com
Action: "sts:AssumeRole"
Path: "/"
Policies:
(...)
#
StepFunctionToHandleVideosResearch:
Type: "AWS::StepFunctions::StateMachine"
Properties:
DefinitionString: !Sub |
{
"StartAt": "Research",
"States": {
"Research": {
"Type": "Task",
"Resource": "${VideoResearch.Arn}",
"End": true
}
}
}
RoleArn: !GetAtt [ StepFunctionToHandleResearchRole, Arn ]
Outputs:
(...)
# I also tried to export the arn of the function
In my function's code I have :
stepFunctionARN = os.environ['STEP_FUNCTION']

Answer 1

#Anthony B. posted the answer in the comments : the problem was related to the fact I added the dependency as global variables, it created a circular dependency (API=> local function <= API looking for function's ARN => doesn't work).
If you remove the global variable and add a local variable, with a "DependsOn: Research" than everything works.
API=>created => creates first function, get Arn => than creates other functions and provide ARN