aws_pubsub_status.py

# Import SDK packages
from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTClient
import boto3
from boto3.dynamodb.conditions import Key, Attr
import jsonconverter as jsonc
import serial
from time import sleep

# Get serial to fetch data from arduino
ser = serial.Serial('/dev/ttyUSB0', 9600)

def customCallback(client, userdata, message):
	print("Received a new message: ")
	print(message.payload)
	print("from topic: ")
	print(message.topic)
	print("--------------\n\n")
	
host = "YOUR HOST NAME"
rootCAPath = "rootca.pem"
certificatePath = "certificate.pem.crt"
privateKeyPath = "private.pem.key"

my_rpi = AWSIoTMQTTClient("basicPubSub")
my_rpi.configureEndpoint(host, 8883)
my_rpi.configureCredentials(rootCAPath, privateKeyPath, certificatePath)

my_rpi.configureOfflinePublishQueueing(-1)  # Infinite offline Publish queueing
my_rpi.configureDrainingFrequency(2)  # Draining: 2 Hz
my_rpi.configureConnectDisconnectTimeout(10)  # 10 sec
my_rpi.configureMQTTOperationTimeout(5)  # 5 sec

# Connect and subscribe to AWS IoT
my_rpi.connect()
my_rpi.subscribe("smartgarden/status", 1, customCallback)
sleep(2)

# Publish to the same topic in a loop forever
loopCount = 0
while True:
  dynamodb = boto3.resource('dynamodb', region_name='us-west-2')
  table = dynamodb.Table('iOweTea-statusData')

  response = table.query(KeyConditionExpression=Key('id').eq('id_status'),
      ScanIndexForward=False
  )

  items = response['Items']

  n=1
  data = items[:n]
  uStatus = data[0]['status']
  status = uStatus.encode('latin-1')
  print(status)
  ser.write(status)
  sleep(4)