aws-step-functions-api.js

// POST /trigger { path: "" }
module.exports.trigger = async (event, context) => {
  const id = uuid();
  await stepfunctions.startExecution({
    stateMachineArn: process.env.STATE_MACHINE_ARN,
    input: JSON.stringify(event.body),
    name: id
  });

  return {
    statusCode: 202,
    headers: {
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      id: id
    })
  };
};

// GET /status?id=...
module.exports.status = async (event, context) => {
  // The Execution ID is given as query string parameter "id"
  const id = event.queryStringParameters.id;
  // The ARN including region, AWS account ID to the step functions execution
  // is stored in the "EXECUTION_ARN" environment variable. We just need to
  // add the execution ID to the end.
  const executionState = await stepfunctions.describeExecution({
    executionArn: process.env.EXECUTION_ARN + id
  }).promise();

  return {
    statusCode: 200,
    headers: {
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      state: executionState.status,
      data: executionState.output
    })
  };
};

serverless.yml

functions:
  trigger:
    handler: handler.trigger
    events:
      - http: POST /trigger
    environment:
      STATE_MACHINE_ARN: "arn:aws:states:#{AWS::Region}:#{AWS::AccountId}:stateMachine:PDFTransform"
  status:
    handler: handler.status
    events:
      - http: GET /trigger
    environment:
      EXECUTION_ARN: "arn:aws:states:#{AWS::Region}:#{AWS::AccountId}:execution:PDFTransform:"