code: def healthz():
      if app.ready:
          return PlainTextResponse("ok")
      return PlainTextResponse(
          "service unavailable",
          status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
      )
  
file_path: cortex/test/apis/batch/sum/app/main.py
imports: import os
  import boto3
  import json
  import re
  from typing import List
  from fastapi import FastAPI, status
  from fastapi.responses import PlainTextResponse
label_desc: Use image node_id 2 for calling a global function with example usage: healthz() and returns: PlainTextResponse, PlainTextResponse