How can i call AWS Step Functions by API Gateway?

Question

I would like to know how to make API Gateway call a Step Function and execute it.

Answer 1

You can create an API Gateway Endpoint with Integration type: AWS Service and set it up to invoke the required Step Function.

In case you want to use API Gateway so that you can control the exposure of your Step Functions endpoint, you can create a new IAM user (programmatic access only) with a policy that only grants access to this endpoint, eg:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "execute-api:Invoke"           
      ],
      "Resource": [
        "arn:aws:execute-api:us-east-1:my-aws-account-id:my-api-id/my-stage/GET/my-resource-path"
      ]
    }
  ]
}  

Answer 2

I think you can use API Gateway Proxy Integration to AWS service. Look: https://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-method-settings-console.html

Answer 3

Consider creating an AWS Lambda function that backs the APIGw endpoint and having it call AWS StepFunctions via code. We use this approach because our use case allows the API endpoint parameters to direct which of several StepFunctions we need to execute.

Admittedly, it is "more code"; we're hoping AWS elaborates StepFunctions such that they can be triggered by the whole host of AWS resource events.

Answer 4

API Gateway added support for Step Functions currently. Now you can create an AWS Service integration via API Gateway Console.

• Integration Type: AWS Service
• AWS Service: Step Functions
• HTTP method: POST
• Action Type: Use action name
• Action: StartExecution
• Execution role: role to start the execution

• Headers:

  X-Amz-Target -> 'AWSStepFunctions.StartExecution'
  Content-Type -> 'application/x-amz-json-1.0'

• Body Mapping Templates/Request payload:

  { "input": "string", "name": "string", "stateMachineArn": "string" }