Google Cloud IoT - Multiple config messages - config

Question

In my code I'm subscribing to 3 different topics:
/devices/{}/config
/devices/{}/events
/devices/{}/state
If I'm not subscribed in /devices/{}/config I don't receive any config message, and that's ok. But if I'm subscribed in /devices/{}/config I get one message for each subscribe I have.
Example:
Subscribed in "/devices/{}/config" and "/devices/{}/events" I get 2 config messages.
Subscribed in "/devices/{}/config" and "/devices/{}/state" I get 2 config messages.
Subscribed in "/devices/{}/config", "/devices/{}/state" and "/devices/{}/events" I get 3 config messages.
Subscribed in "/devices/{}/events" and "/devices/{}/state" I get 0 config messages.
This is causing error in IoT core: mqtt:
The device "xxxxxxxx" could not be updated. Device state can be updated only once every 1s.
In fact i want and need just one config message. What am I doing wrong?
This is my code:
# [START iot_mqtt_includes]
import argparse
import datetime
import os
import random
import ssl
import time
import log
import updateConfig
import jwt
import paho.mqtt.client as mqtt
import payload
# [END iot_mqtt_includes]
# The initial backoff time after a disconnection occurs, in seconds.
minimum_backoff_time = 1
# The maximum backoff time before giving up, in seconds.
MAXIMUM_BACKOFF_TIME = 32
# Whether to wait with exponential backoff before publishing.
should_backoff = False
# [START iot_mqtt_jwt]
def create_jwt(project_id, private_key_file, algorithm):
token = {
# The time that the token was issued at
'iat': datetime.datetime.utcnow(),
# The time the token expires.
'exp': datetime.datetime.utcnow() + datetime.timedelta(minutes=60),
# The audience field should always be set to the GCP project id.
'aud': project_id
}
# Read the private key file.
with open(private_key_file, 'r') as f:
private_key = f.read()
f.close()
return jwt.encode(token, private_key, algorithm=algorithm)
# [END iot_mqtt_jwt]
# [START iot_mqtt_config]
def error_str(rc):
"""Convert a Paho error to a human readable string."""
return '{}: {}'.format(rc, mqtt.error_string(rc))
def on_connect(unused_client, unused_userdata, unused_flags, rc):
"""Callback for when a device connects."""
log.append_log('ao_conectar - ' + mqtt.connack_string(rc))
# After a successful connect, reset backoff time and stop backing off.
global should_backoff
global minimum_backoff_time
should_backoff = False
minimum_backoff_time = 1
def on_disconnect(unused_client, unused_userdata, rc):
"""Paho callback for when a device disconnects."""
append_log('ao_desconectar - '+ error_str(rc))
# Since a disconnect occurred, the next loop iteration will wait with
# exponential backoff.
global should_backoff
should_backoff = True
def on_publish(unused_client, unused_userdata, unused_mid):
"""Paho callback when a message is sent to the broker."""
def on_message(unused_client, unused_userdata, message):
"""Callback when the device receives a message on a subscription."""
config = str(message.payload)
retorno = updateConfig.update(config)
def get_client(
project_id, cloud_region, registry_id, device_id, private_key_file,
algorithm, ca_certs, mqtt_bridge_hostname, mqtt_bridge_port):
"""Create our MQTT client. The client_id is a unique string that identifies
this device. For Google Cloud IoT Core, it must be in the format below."""
client = mqtt.Client(
client_id=('projects/{}/locations/{}/registries/{}/devices/{}'
.format(
project_id,
cloud_region,
registry_id,
device_id)))
# With Google Cloud IoT Core, the username field is ignored, and the
# password field is used to transmit a JWT to authorize the device.
client.username_pw_set(
username='unused',
password=create_jwt(
project_id, private_key_file, algorithm))
# Enable SSL/TLS support.
client.tls_set(ca_certs=ca_certs, tls_version=ssl.PROTOCOL_TLSv1_2)
# Register message callbacks. https://eclipse.org/paho/clients/python/docs/
# describes additional callbacks that Paho supports. In this example, the
# callbacks just print to standard out.
client.on_connect = on_connect
client.on_publish = on_publish
client.on_disconnect = on_disconnect
client.on_message = on_message
# Connect to the Google MQTT bridge.
client.connect(mqtt_bridge_hostname, mqtt_bridge_port)
# This is the topic that the device will receive configuration updates on.
mqtt_config_topic = '/devices/{}/config'.format(device_id)
# Subscribe to the config topic.
client.subscribe(mqtt_config_topic, qos=1)
return client
# [END iot_mqtt_config]
def parse_command_line_args():
"""Parse command line arguments."""
parser = argparse.ArgumentParser(description=(
'Example Google Cloud IoT Core MQTT device connection code.'))
parser.add_argument(
'--project_id',
default=os.environ.get('GOOGLE_CLOUD_PROJECT'),
help='GCP cloud project name')
parser.add_argument(
'--registry_id', required=True, help='Cloud IoT Core registry id')
parser.add_argument(
'--device_id', required=True, help='Cloud IoT Core device id')
parser.add_argument(
'--private_key_file',
required=True, help='Path to private key file.')
parser.add_argument(
'--algorithm',
choices=('RS256', 'ES256'),
required=True,
help='Which encryption algorithm to use to generate the JWT.')
parser.add_argument(
'--cloud_region', default='us-central1', help='GCP cloud region')
parser.add_argument(
'--ca_certs',
default='roots.pem',
help=('CA root from https://pki.google.com/roots.pem'))
parser.add_argument(
'--message_type',
choices=('event', 'state'),
default='event',
help=('Indicates whether the message to be published is a '
'telemetry event or a device state message.'))
parser.add_argument(
'--mqtt_bridge_hostname',
default='mqtt.googleapis.com',
help='MQTT bridge hostname.')
parser.add_argument(
'--mqtt_bridge_port',
choices=(8883, 443),
default=8883,
type=int,
help='MQTT bridge port.')
parser.add_argument(
'--jwt_expires_minutes',
default=20,
type=int,
help=('Expiration time, in minutes, for JWT tokens.'))
return parser.parse_args()
# [START iot_mqtt_run]
def main():
log.append_log("Iniciando uma nova conexao com o Google IoT.")
global minimum_backoff_time
args = parse_command_line_args()
# Publish to the events or state topic based on the flag.
jwt_iat = datetime.datetime.utcnow()
jwt_exp_mins = args.jwt_expires_minutes
client = get_client(
args.project_id, args.cloud_region, args.registry_id, args.device_id,
args.private_key_file, args.algorithm, args.ca_certs,
args.mqtt_bridge_hostname, args.mqtt_bridge_port)
# Publish num_messages mesages to the MQTT bridge once per second.
while True:
# Process network events.
client.loop()
# Wait if backoff is required.
if should_backoff:
# If backoff time is too large, give up.
if minimum_backoff_time > MAXIMUM_BACKOFF_TIME:
log.append_log('Tempo maximo de backoff excedido. Desistindo.')
break
# Otherwise, wait and connect again.
delay = minimum_backoff_time + random.randint(0, 1000) / 1000.0
log.append_log('Esperando {} segundos antes de reconectar.'.format(delay))
time.sleep(delay)
minimum_backoff_time *= 2
client.connect(args.mqtt_bridge_hostname, args.mqtt_bridge_port)
# [START iot_mqtt_jwt_refresh]
seconds_since_issue = (datetime.datetime.utcnow() - jwt_iat).seconds
if seconds_since_issue > 60 * jwt_exp_mins:
log.append_log('Atualizando token de acesso depois de {} segundos'.format(seconds_since_issue))
client.loop_stop()
jwt_iat = datetime.datetime.utcnow()
client = get_client(
args.project_id, args.cloud_region,
args.registry_id, args.device_id, args.private_key_file,
args.algorithm, args.ca_certs, args.mqtt_bridge_hostname,
args.mqtt_bridge_port)
# [END iot_mqtt_jwt_refresh]
# Publish "payload" to the MQTT topic. qos=1 means at least once
# delivery. Cloud IoT Core also supports qos=0 for at most once
# delivery.
payloadToPublish = payload.lerPayload()
if payloadToPublish != 'sem payload':
if payloadToPublish[0] == 'event':
mqtt_topic = '/devices/{}/{}'.format(args.device_id, 'events')
log.append_log('publicando [' + payloadToPublish[1] + ']')
else:
mqtt_topic = '/devices/{}/{}'.format(args.device_id, 'state')
client.publish(mqtt_topic, payloadToPublish[1], qos=1)
# [END iot_mqtt_run]
if __name__ == '__main__':
main()

Answer 1

This is the expected behavior:
The event and state topic are used for device to cloud communication and the config topic is used for sending configuration data to an IoT device. Subscribing to the events / state topics is effectively a NOOP.
Cloud IoT Core only supports QoS 1, which is "at least once" for message transmission, you may want to try QoS 0, which does not retry message transmission until ACK but I don't think this is what you want
STATE and CONFIG transmission is limited to a single message per second; transmitting configuration changes faster than this will cause the error you're seeing