Now AWS IoT Core allows Users to Save Messages for Disconnected Devices

Now you can begin to connect your devices to AWS IoT Core with the help of Persistent Sessions. Persistent Sessions save subscription data and undone Quality of Service (QoS) one messages should the devices become disconnected. When a device rejoins and restarts a Persistent Session, its subscriptions will be automatically restored and any saved messages will be delivered. Persistent Sessions are a standard MQTT 3.1.1 feature, and are started with the use of CleanSession flag when joining. This flag is supported by AWS IoT Device SDKs and most other MQTT clients. These Persistent Sessions are accessible in each regions where AWS IoT Core is accessible. To get more information; refer Developer Guide