Today, managing communication between the cloud and millions of smart devices is challenging.  Suppose you are managing a huge number of devices out there and you need to push some critical device state update to them all, but many of them are offline or may have spotty network issues; how do you make sure this message gets through?

The Azure IoT Hub provides three major cloud-to-device communication mechanisms: C2D messages, direct methods, and desired properties in the device twin. These are each designed for different use cases. This article presents how to effectively select these methods to build reliable, scalable, and effective IoT solutions. Knowing the details when to use each one for what scenarios will help to build robust and reliable IOT solutions.