how to run mqtt in flask application simultaneously over wsgi - flask

Question

I created a flask application that consists of MQTT client which simultaneously subscribe data from esp32 and store it in database.
from flask import Flask, redirect, render_template, request, session, abort,make_response,jsonify, flash, url_for
import paho.mqtt.client as mqtt
import json
import config
import db_access
#mqtt code
def on_message(client, userdata, message):
topic = message.topic
print("line 12 - topic checkpoint - ",topic)
msgDecode=str(message.payload.decode("utf-8","ignore"))
msgJson=json.loads(msgDecode) #decode json data
print("line 15 - json checkpoint - ",type(msgJson))
# deviceID = msgJson["DeviceID"]
# currentCounter = msgJson["Counter"]
# status = msgJson["Status"]
db_access.updateStatus(msgJson["DeviceID"],msgJson["Status"])
app = Flask(__name__,template_folder='templates')
'''Web portal routes'''
#app.route('/device/switch', methods=['POST'])
def switch():
#parameter parsing
deviceID = request.args.get('deviceID')
status = request.args.get('status')
statusMap = {"on":1,"off":0}
#MQTT publish
mqtt_msg = json.dumps({"deviceID":int(deviceID),"status":statusMap[status]})
client.publish(config.MQTT_STATUS_CHANGE_TOPIC,mqtt_msg)
time_over_flag = 0
loop_Counter = 0
while status != db_access.getDeviceStatus(deviceID):
time.sleep(2)
loop_Counter+=1
if loop_Counter ==2:
time_over_flag = 1
break
if time_over_flag:
return make_response(jsonify({"statusChange":False}))
else:
return make_response(jsonify({"statusChange":True}))
if __name__ == "__main__":
db_access.createUserTable()
db_access.insertUserData()
db_access.createDeviceTable()
db_access.insertDeviceData()
print("creating new instance")
client = mqtt.Client("server") #create new instance
client.on_message=on_message #attach function to callback
print("connecting to broker")
client.connect(config.MQTT_BROKER_ADDRESS)
client.loop_start()
print("Subscribing to topic","esp/#")
client.subscribe("esp/#")
app.run(debug=True, use_reloader=False)
This is code in ____init____.py
db_access.py is consist of database operations and config.py consist of configurations.
Will this work in apache?
also, I have no previous experience with WSGI

Answer 1

The problem with launching your code (as included) with a WSGI server, is the part in that last if block, only gets run when you execute that file directly with the python command.
To make this work, I'd try moving that block of code to the top of your file, around here:
app = Flask(__name__,template_folder='templates')
db_access.createUserTable()
db_access.insertUserData()
db_access.createDeviceTable()
db_access.insertDeviceData()
print("creating new instance")
client = mqtt.Client("server") #create new instance
client.on_message=on_message #attach function to callback
print("connecting to broker")
client.connect(config.MQTT_BROKER_ADDRESS)
client.loop_start()
print("Subscribing to topic","esp/#")
client.subscribe("esp/#")
I'd also rename that __init__.py file, to something like server.py as the init file isn't meant to be heavy.
Once you've done that, run it with the development server again and test that it works as expected.
Then install a WSGI server like gunicorn into your virtual enviornment:
pip install gunicorn
And launch the app with gunicorn (this command should work, assuming you renamed your file to server.py):
gunicorn --bind '0.0.0.0:5000' server:app
Then test again.