Pywin32 service fails to start, unable to read json file - python-3.x

Question

I used the Pywin32 tools and NSSM to create a windows service for my Flask application. I noticed that the service wouldn't start giving me a message :
The service did not return an error. This could be an internal Windows error or an internal service error
I noticed that when I removed all reference to a config.json file(used to connect to the DB) the created service starts. My service.py is :
import win32serviceutil
import win32service
import win32event
import servicemanager
from multiprocessing import Process
from app import app
class Service(win32serviceutil.ServiceFramework):
_svc_name_ = "TestService"
_svc_display_name_ = "Test Service"
_svc_description_ = "Tests Python service framework by receiving and echoing messages over a named pipe"
def __init__(self, *args):
super().__init__(*args)
def SvcStop(self):
self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
self.process.terminate()
self.ReportServiceStatus(win32service.SERVICE_STOPPED)
def SvcDoRun(self):
self.process = Process(target=self.main)
self.process.start()
self.process.run()
def main(self):
app.run()
if __name__ == '__main__':
if len(sys.argv) == 1:
servicemanager.Initialize()
servicemanager.PrepareToHostSingle(RouterService)
servicemanager.StartServiceCtrlDispatcher()
else:
win32serviceutil.HandleCommandLine(RouterService)
The following sample implementation of app.py works :
from flask import Flask
import json
import socket
app = Flask(__name__)
host = "<IP>"
user = "<username>"
passwd = "XXXXX"
DB = "YYYYY"
#app.route('/')
def hello_world():
return 'Hello, World!'
app.run(host = "0.0.0.0",debug = False, port=9000, threaded=True)
But as soon as I add code to read the DB credentials from a config.json file, the created service gives me an error :
conf = open('.\\config.json', "r")
data = json.loads(conf.read())
db_conf = data['db_connection']
host = db_conf['host']
user = db_conf['username']
passwd = db_conf['password']
DB = db_conf['DB']
Are there any issues with pywin32 reading json files? When I run the same app.py file from the command prompt it reads all the json files and runs without issues.