Azure IoT Edge Offline capabilities Example - azure-iot-hub

Question

I'm a little bit confused on how to use IoT Edge Offline mode. I though it was out-of-box!
The location of my IoT Hub is in West US. When I disconnect my Edge device from the network nothing happen. The datas is not saved or resend after reconnecting it online.
I got only one module that send data to the IoT Hub, I can see the datas flowing with Device Explorer Twin app and I saved the data in a database.
After disconnecting, wait 5 minutes and reconnecting, I don't see the datas that I was trying to send during offline mode in the database.
All messages while offline are missing (I'm sequencing the message with datetime stamp).
Did I missed a configuration?
Any idea why the offline mode doesn't work for me?
I'm using Iot Edge Runtime v1.0.6 and Windows Containers.
Here the source code of my testing module:
using Microsoft.Azure.Devices.Client;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Runtime.Loader;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
class Program
{
static int monitoringInterval { get; set; } = 60;// 60 seconds
static System.Timers.Timer testTimer;
static ModuleClient ioTHubModuleClient;
static void Main(string[] args)
{
Init().Wait();
StartTestTimer();
// Wait until the app unloads or is cancelled
var cts = new CancellationTokenSource();
AssemblyLoadContext.Default.Unloading += (ctx) => cts.Cancel();
Console.CancelKeyPress += (sender, cpe) => cts.Cancel();
WhenCancelled(cts.Token).Wait();
}
/// <summary>
/// Handles cleanup operations when app is cancelled or unloads
/// </summary>
public static Task WhenCancelled(CancellationToken cancellationToken)
{
var tcs = new TaskCompletionSource<bool>();
cancellationToken.Register(s => ((TaskCompletionSource<bool>)s).SetResult(true), tcs);
return tcs.Task;
}
/// <summary>
/// Initializes the ModuleClient and sets up the callback to receive
/// messages containing temperature information
/// </summary>
static async Task Init()
{
AmqpTransportSettings amqpSetting = new AmqpTransportSettings(TransportType.Amqp_Tcp_Only);
ITransportSettings[] settings = { amqpSetting };
// Open a connection to the Edge runtime
ioTHubModuleClient = await ModuleClient.CreateFromEnvironmentAsync(settings);
await ioTHubModuleClient.OpenAsync();
Console.WriteLine("IoT Hub module client initialized.");
}
static void StartTestTimer()
{
Console.WriteLine("Start Monitoring Timer: " + monitoringInterval + " seconds");
// Set up a timer that triggers every minute.
testTimer = new System.Timers.Timer();
testTimer.Interval = monitoringInterval * 1000; // 60 seconds
testTimer.Elapsed += new System.Timers.ElapsedEventHandler(SendEvent);
testTimer.Start();
SendEvent(null, null);
}
async static void SendEvent(object sender, System.Timers.ElapsedEventArgs args)
{
DateTime today = DateTime.Now;
Console.WriteLine("[" + today + "] Send Data has started...");
try
{
//IoT device connection string
string connectionString = "HostName=xxxxxx.azure-devices.net;DeviceId=IOT-Device1;SharedAccessKey=ett8xxxxxxxxx";
// Connect to the IoT hub using the MQTT protocol
DeviceClient _DeviceClient = DeviceClient.CreateFromConnectionString(connectionString, TransportType.Mqtt);
_DeviceClient.OperationTimeoutInMilliseconds = 10000;
Dictionary<string, Object> telemetryDataPoint = new Dictionary<string, Object>();
string dateTime = DateTime.Now.ToLongDateString() + " " + DateTime.Now.ToLongTimeString();
telemetryDataPoint.Add("DateTime", dateTime);
string messageString = JsonConvert.SerializeObject(telemetryDataPoint);
Message message = new Message(Encoding.ASCII.GetBytes(messageString));
// Send the telemetry message
Console.WriteLine("\n*> Sending message: {0}", messageString);
await _DeviceClient.SendEventAsync(message).ConfigureAwait(false);
Console.WriteLine("Message sent!");
}
catch (Exception e)
{
Console.WriteLine("Message not sent. Connection error to Iot Hub:" + e.Message);
}
}
}

Answer 1

Why is the code creating a moduleClient in Init(), but then attempting to send an a message directly to IoT Hub using a deviceClient in SendEvent()? This bypasses the edge runtime (specifically edgeHub) completely which is what facilitates offline store and forward.
Here is an example of the right way to do this: https://github.com/Azure/iotedge/blob/ad41fec507bb91a2e57a07cd32e287ada0ca08d8/edge-modules/SimulatedTemperatureSensor/src/Program.cs#L95