I am publishing ESP data to Google Cloud IOT via MQTT to a particular topic. But If I have many devices data, then is it necessary to create different topic for each device? If Yes, then how can I trigger a single cloud function for multiple topics. I couldn't find it anywhere on the Google Cloud Platform Documentation. So please help me!.
No, the message contain the attributes of your device. Like this, you can know the context of the message and process all the messages by the same Cloud Functions.