AWS IoT MQTT Client for Python - How do you subscribe forever? - infinite-loop

Question

I'm using the example from the samples/basicPubSub/basicPubSub.py with useWebsocket=True
I have some file my_test_file.py where I connect() and subscribe() with a message callback. Let's say the callback just writes to some log file. How can I have this file always be running, so that if I publish from somewhere else, today, tomorrow, a year from now - this log file is constantly being written to with the message?
from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTClient
client = AWSIoTMQTTClient('client_id', useWebsocket=True)
client.configureEndpoint('host', port)
client.configureCredentials('path to cert')
client.configureAutoReconnectBackoffTime(1, 32, 20)
client.configureOfflinePublishQueueing(-1)
client.configureDrainingFrequency(2)
client.configureConnectDisconnectTimeout(10)
client.configureMQTTOperationTimeout(5)
client.connect()
client.subscribe('topic name', 1, _some_callback_func)
while True:
time.sleep(1)
Is having an infinite while loop at the end of my_test_file.py the only way? With the infinite while loop, I run the file and it's a blocking process, but it is infinitely subscribed. Is it a combination of a systemd service and this infinite while loop? I saw some loop_forever() methods in the Paho MQTT client, does the aws iot mqtt client have something similar? Is loop_forever() just implementing an infinite while loop?

Answer 1

Infinite looping is the right way to handle with that, as long as you know what to do, not interrupting the main process (core logic). To do so, I recommend you isolate this script in a new python file to be runned by the main python script as a subprocess. So, before you start with hands on, read Multiprocessing - process-based parallelism.
Usually something always need to keeping the Python process running on memory, unless something reboot the OS unexpectedly.
It seems not be an elegant way to handle with it, but I advise you to construct an execution management structure behind this Python script, like always initiate your python script after "boot loader" machine/device, make an another watchdog script, or something else like that, to prevent some internet connections problems, forcing the system to be rebooted or reconnect to the internet.