TTI V3 Connector Azure Storage Queues

The first Proof of Concept(PoC) for my updated The Things Industries(TTI) V3 Webhooks Integration was to explore the use of Azure Functions to securely ingest webhook calls. The aim was to have uplink and downlink message progress message payloads written to Azure Storage Queues with output bindings ready for processing.

namespace devMobile.IoT.TheThingsIndustries.HttpInputStorageQueueOutput
{
	using System.Net;
	using System.Threading.Tasks;

	using Microsoft.Azure.Functions.Worker;
	using Microsoft.Azure.Functions.Worker.Http;
	using Microsoft.Azure.WebJobs;
	using Microsoft.Extensions.Logging;


	[StorageAccount("AzureWebJobsStorage")]
	public static class Webhooks
	{
		[Function("Uplink")]
		public static async Task<HttpTriggerUplinkOutputBindingType> Uplink([HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequestData req, FunctionContext context)
		{
			var logger = context.GetLogger("UplinkMessage");

			logger.LogInformation("Uplink processed");
			
			var response = req.CreateResponse(HttpStatusCode.OK);

			return new HttpTriggerUplinkOutputBindingType()
			{
				Name = await req.ReadAsStringAsync(),
				HttpReponse = response
			};
		}

		public class HttpTriggerUplinkOutputBindingType
		{
			[QueueOutput("uplink")]
			public string Name { get; set; }

			public HttpResponseData HttpReponse { get; set; }
		}

...

		[Function("Failed")]
		public static async Task<HttpTriggerFailedOutputBindingType> Failed([HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequestData req, FunctionContext context)
		{
			var logger = context.GetLogger("Failed");

			logger.LogInformation("Failed procssed");

			var response = req.CreateResponse(HttpStatusCode.OK);

			return new HttpTriggerFailedOutputBindingType()
			{
				Name = await req.ReadAsStringAsync(),
				HttpReponse = response
			};
		}

		public class HttpTriggerFailedOutputBindingType
		{
			[QueueOutput("failed")]
			public string Name { get; set; }

			public HttpResponseData HttpReponse { get; set; }
		}
	}
}

After some initial problems with the use of Azure Storage Queue output bindings to insert messages into the ack, nak, failed, queued, and uplink Azure Storage Queues I found it didn’t take much code and worked reliably on my desktop.

Azure Functions Desktop Development environment running my functions

I used Telerik Fiddler with some sample payloads to test my application.

Telerik Fiddler Request Composer “posting” sample message to desktop endpoint

Once the functions were running reliably on my desktop, I created an Azure Service Plan, deployed the code, then generated an API Key for securing my HTTPTrigger endpoints.

Azure Functions Host Key configuration dialog

I then added a TTI Webhook Integration to my TTI SeeduinoLoRaWAN application, manually configured the endpoint, enabled the different messages I wanted to process and set the x-functions-key header.

TTI Application Webhook configuration

After a short delay I could see messages in the message uplink queue with Azure Storage Explorer

Azure Storage Explorer displaying content of my uplink queue

Building a new version of my TTIV3 Azure IoT connector is a useful learning exercise but I’m still deciding whether is it worth the effort as TTI has one now?

Azure HTTP Trigger Functions with .NET Core 5

My updated The Things Industries(TTI) connector will use a number of Azure Functions to process Application Integration webhooks (with HTTP Triggers) and Azure Storage Queue messages(with Output Bindings & QueueTriggers).

On a couple of customer projects we had been updating Azure Functions from .NET 4.X to .NET Core 3.1, and most recently .NET Core 5. This process has been surprisingly painful so I decided to build a series of small proof of concept (PoC) projects to explore the problem.

Visual Studio Azure Function Trigger type selector

I started with the Visual Studio 2019 Azure Function template and created a plain HTTPTrigger.

public static class Function1
{
   [Function("Function1")]
   public static HttpResponseData Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req,
      FunctionContext executionContext)
   {
      var logger = executionContext.GetLogger("Function1");
      logger.LogInformation("C# HTTP trigger function processed a request.");

      var response = req.CreateResponse(HttpStatusCode.OK);
      response.Headers.Add("Content-Type", "text/plain; charset=utf-8");

      response.WriteString("Welcome to Azure Functions!");

      return response;
   }
}

I changed the AuthorizationLevel to Anonymous to make testing in Azure with Telerik Fiddler easier

public static class Function1
{
	[Function("PlainAsync")]
	public static async Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequestData request, FunctionContext executionContext)
	{
		var logger = executionContext.GetLogger("UplinkMessage");

		logger.LogInformation("C# HTTP trigger function processed a request.");

		var response = request.CreateResponse(HttpStatusCode.OK);

		response.Headers.Add("Content-Type", "text/plain; charset=utf-8");

		response.WriteString("Welcome to Azure Functions!");

		return new OkResult();
	}
}

With not a lot of work I had an Azure Function I could run in the Visual Studio debugger

Azure Functions Debug Diagnostic Output

I could invoke the function using the endpoint displayed as debugging environment started.

Telerik Fiddler Composer invoking Azure Function running locally

I then added more projects to explore asynchronicity, and output bindings

Azure Functions Solution PoC Projects

After a bit of “trial and error” I had an HTTPTrigger Function that inserted a message containing the payload of an HTTP POST into an Azure Storage Queue.

[StorageAccount("AzureWebJobsStorage")]
public static class Function1
{
	[Function("Uplink")]
	public static async Task<HttpTriggerUplinkOutputBindingType> Uplink([HttpTrigger(AuthorizationLevel.Function, "post")] HttpRequestData req, FunctionContext context)
	{
		var logger = context.GetLogger("UplinkMessage");

		logger.LogInformation("Uplink processed");
			
		var response = req.CreateResponse(HttpStatusCode.OK);

		return new HttpTriggerUplinkOutputBindingType()
		{
			Name = await req.ReadAsStringAsync(),
			HttpReponse = response
		};
	}

	public class HttpTriggerUplinkOutputBindingType
	{
		[QueueOutput("uplink")]
		public string Name { get; set; }

		public HttpResponseData HttpReponse { get; set; }
	}
}

The key was Multiple Output Bindings so the function could return a result for both the HttpResponseData and Azure Storage Queue operations

Azure Functions Debug Diagnostic Output

After getting the function running locally I deployed it to a Function App running in an App Service plan

Azure HTTP Trigger function Host Key configuration

Using the Azure Portal I configured an x-functions-key which I could use in Telerik Fiddler

After fixing an accidental truncation of the x-functions-key a message with the body of the POST was created in the Azure Storage Queue.

Azure Storage Queue Message containing HTTP Post Payload

The aim of this series of PoCs was to have an Azure function that securely (x-functions-key) processed an Hyper Text Transfer Protocol(HTTP) POST with an HTTPTrigger and inserted a message containing the payload into an Azure Storage Queue using an OutputBinding.

Use the contents of this blog post with care as it may not age well.

TTN V3 Connector Revisited

Earlier in the year I built Things Network(TTN) V2 and V3 connectors and after using these in production applications I have learnt a lot about what I had got wrong, less wrong and what I had got right.

Using a TTN V3 MQTT Application integration wasn’t a great idea. The management of state was very complex. The storage of application keys in a app.settings file made configuration easy but was bad for security.

The use of Azure Key Vault in the TTNV2 connector was a good approach, but the process of creation and updating of the settings needs to be easier.

Using TTN device registry as the “single source of truth” was a good decision as managing the amount of LoRaWAN network, application and device specific configuration in an Azure IoT Hub would be non-trivial.

Using a Webhooks Application Integration like the TTNV2 connector is my preferred approach.

The TTNV2 Connector’s use of Azure Storage Queues was a good idea as they it provide an elastic buffer between the different parts of the application.

The use of Azure Functions to securely ingest webhook calls and write them to Azure Storage Queues with output bindingts should simplify configuration and deployment. The use of Azure Storage Queue input bindings to process messages is the preferred approach.

The TTN V3 processing of JSON uplink messages into a structure that Azure IoT Central could ingest is a required feature

The TTN V2 and V3 support for the Azure Device Provisioning Service(DPS) is a required feature (mandated by Azure IoT Central). The TTN V3 connector support for DTDLV2 is a desirable feature. The DPS implementation worked with Azure IoT Central but I was unable to get the DeviceClient based version working.

Using DPS to pre-provision devices in Azure IoT Hubs and Azure IoT Central by using the TTN Application Registry API then enumerating the TTN applications, then devices needs to be revisited as it was initially slow then became quite complex.

The support for Azure IoT Hub connection strings was a useful feature, but added some complexity. This plus basic Azure IoT Hub DPS support(No Azure IoT Central support) could be implemented in a standalone application which connects via Azure Storage Queue messages.

The processing of Azure IoT Central Basic, and Request commands then translating the payloads so they work with TTN V3 is a required feature. The management of Azure IoT Hub command delivery confirmations (abandon, complete and Reject) is a required feature.

I’m considering building a new TTN V3 connector but is it worth the effort as TTN has one now?

Azure Functions with VB.Net 4.X

As part of my “day job” I spend a lot of time working with C# and VB.Net 4.X “legacy” projects doing upgrades, bugs fixes and moving applications to Azure. For the last couple of months I have been working on a project replacing Microsoft message queue(MSMQ) queues with Azure Storage Queues so the solution is easier to deploy in Azure.

The next phase of the project is to replace a number of Windows Services with Azure Queue Trigger and Timer Trigger functions. The aim is a series of small steps which we can test before deployment rather than major changes, hence the use of V1 Azure functions for the first release.

Silver Fox systems sells a Visual Studio extension which generates an HTTP Trigger VB.Net project. I needed Timer and Queue Trigger functions so I created C# examples and then used them to figure out how to build VB.Net equivalents

Visual Studio Solution Explorer

After quite a few failed attempts I found this sequence worked for me

Add a new VB.Net class library
Provide a name for new class library
Select target framework

Even though the target platform is not .NET 5.0 ignore this and continue.

Microsoft.NET.Sdk.Functions

Added Microsoft.NET.Sdk.Functions (make sure version 1.0.38)

Visual Studio project with Azure Function Icon.

Then unload the project and open the file.

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <RootNamespace>TimerClass</RootNamespace>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="1.0.38" />
  </ItemGroup>

</Project>

Add the TargetFramework and AzureFunctionsVersion lines

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <RootNamespace>TimerClass</RootNamespace>
    <TargetFramework>net48</TargetFramework>
    <AzureFunctionsVersion>v1</AzureFunctionsVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="1.0.38" />
  </ItemGroup>

</Project>

At this point the project should compile but won’t do much, so update the class to look like the code below.

Imports System.Threading

Imports Microsoft.Azure.WebJobs
Imports Microsoft.Extensions.Logging


Public Class TimerTrigger
   Shared executionCount As Int32

   <FunctionName("Timer")>
   Public Shared Sub Run(<TimerTrigger("0 */1 * * * *")> myTimer As TimerInfo, log As ILogger)
      Interlocked.Increment(executionCount)

      log.LogInformation("VB.Net TimerTrigger next trigger:{0} Execution count:{1}", myTimer.ScheduleStatus.Next, executionCount)

   End Sub
End Class

Then add an empty hosts.json file (make sure “copy if newer” is configured in properties) to the project directory, then depending on deployment model configure the AzureWebJobsStorage and AzureWebJobsDashboard connection strings via environment variables or a local.settings.json file.

Visual Studio Environment variables for AzureWebJobsStorage and AzureWebJobsDashboard connection strings

Blob Trigger Sample code

Imports System.IO
Imports System.Threading

Imports Microsoft.Azure.WebJobs
Imports Microsoft.Extensions.Logging


Public Class BlobTrigger
   Shared executionCount As Int32

   ' This function will get triggered/executed when a new message is written on an Azure Queue called events.
   <FunctionName("Notifications")>
   Public Shared Async Sub Run(<BlobTrigger("notifications/{name}", Connection:="BlobEndPoint")> payload As Stream, name As String, log As ILogger)
      Interlocked.Increment(executionCount)

      log.LogInformation("VB.Net BlobTrigger processed blob name:{0} Size:{1} bytes Execution count:{2}", name, payload.Length, executionCount)
   End Sub
End Class

HTTP Trigger Sample code

Imports System.Net
Imports System.Net.Http
Imports System.Threading

Imports Microsoft.Azure.WebJobs
Imports Microsoft.Azure.WebJobs.Extensions.Http
Imports Microsoft.Extensions.Logging


Public Class HttpTrigger
   Shared executionCount As Int32

   <FunctionName("Notifications")>
   Public Shared Async Function Run(<HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route:=Nothing)> req As HttpRequestMessage, log As ILogger) As Task(Of HttpResponseMessage)
      Interlocked.Increment(executionCount)

      log.LogInformation($"VB.Net HTTP trigger Execution count:{0} Method:{1}", executionCount, req.Method)

      Return New HttpResponseMessage(HttpStatusCode.OK)
   End Function
End Class

Queue Trigger Sample Code

Imports System.Threading

Imports Microsoft.Azure.WebJobs
Imports Microsoft.Extensions.Logging


Public Class QueueTrigger
   Shared ConcurrencyCount As Long
   Shared ExecutionCount As Long

   <FunctionName("Alerts")>
   Public Shared Sub ProcessQueueMessage(<QueueTrigger("notifications", Connection:="QueueEndpoint")> message As String, log As ILogger)
      Interlocked.Increment(ConcurrencyCount)
      Interlocked.Increment(ExecutionCount)

      log.LogInformation("VB.Net Concurrency:{0} Message:{1} Execution count:{2}", ConcurrencyCount, message, ExecutionCount)

      ' Wait for a bit to force some consurrency
      Thread.Sleep(5000)

      Interlocked.Decrement(ConcurrencyCount)
   End Sub
End Class

As well as counting the number of executions I also wanted to check that >1 instances were started to process messages when the queues had many messages. I added a “queues” section to the hosts.json file so I could tinker with the options.

{
  "queues": {
    "maxPollingInterval": 100,
    "visibilityTimeout": "00:00:05",
    "batchSize": 16,
    "maxDequeueCount": 5,
    "newBatchThreshold": 8
  }
}

The QueueMessageGenerator application inserts many messages into a queue for processing.

When I started the QueueTrigger function I could see the concurrency count was > 0

Timer Trigger Sample Code

Imports System.Threading

Imports Microsoft.Azure.WebJobs
Imports Microsoft.Extensions.Logging


Public Class TimerTrigger
   Shared executionCount As Int32

   <FunctionName("Timer")>
   Public Shared Sub Run(<TimerTrigger("0 */1 * * * *")> myTimer As TimerInfo, log As ILogger)
      Interlocked.Increment(executionCount)

      log.LogInformation("VB.Net TimerTrigger next trigger:{0} Execution count:{1}", myTimer.ScheduleStatus.Next, executionCount)

   End Sub
End Class

The source code for the C# and VB.Net functions is available on GitHub

TTI V3 Connector Device EUI Representation

While debugging The Things Industries(TTI) V3 connector on my desktop I had noticed the Device EUI‘s were wrong.

TTI V3 Connector application running as a console application showing incorrect DeviceEUIs

The TTI V3 Connector code…

foreach (V3EndDevice device in endDevices.End_devices)
{
   if (DeviceAzureEnabled(device))
   {
      _logger.LogInformation("Config-ApplicationID:{0} DeviceID:{1} Device EUI:{2}", device.Ids.Application_ids.Application_id, device.Ids.Device_id, BitConverter.ToString(device.Ids.Dev_eui));

      tasks.Add(DeviceRegistration(device.Ids.Application_ids.Application_id, device.Ids.Device_id, _programSettings.ResolveDeviceModelId(device.Ids.Application_ids.Application_id, device.Attributes), stoppingToken));
   }
}

…uses some classes generated by nSwag based on the TheThingsNetwork/LoRaWAN-stack api.swagger.json

public partial class V3EndDeviceIdentifiers 
{
        [Newtonsoft.Json.JsonProperty("device_id", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Device_id { get; set; }
    
        [Newtonsoft.Json.JsonProperty("application_ids", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public V3ApplicationIdentifiers Application_ids { get; set; }
    
        /// <summary>The LoRaWAN DevEUI.</summary>
        [Newtonsoft.Json.JsonProperty("dev_eui", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public byte[] Dev_eui { get; set; }
    
        /// <summary>The LoRaWAN JoinEUI (AppEUI until LoRaWAN 1.0.3 end devices).</summary>
        [Newtonsoft.Json.JsonProperty("join_eui", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public byte[] Join_eui { get; set; }
    
        /// <summary>The LoRaWAN DevAddr.</summary>
        [Newtonsoft.Json.JsonProperty("dev_addr", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public byte[] Dev_addr { get; set; }
}

After some research I found references to the underlying problem in TTN and OpenAPI forums. The Dev_addr and Dev_eui fields are Base16(Hexidecimal) encoded binary but are being processed as if they were Base64(mime) encoded.

The TTI connector only displays the Device EUI so I changed the Dev_eui property to a string

public partial class V3EndDeviceIdentifiers 
{
        [Newtonsoft.Json.JsonProperty("device_id", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Device_id { get; set; }
    
        [Newtonsoft.Json.JsonProperty("application_ids", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public V3ApplicationIdentifiers Application_ids { get; set; }
    
        /// <summary>The LoRaWAN DevEUI.</summary>
        [Newtonsoft.Json.JsonProperty("dev_eui", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public string Dev_eui { get; set; }

      /// <summary>The LoRaWAN JoinEUI (AppEUI until LoRaWAN 1.0.3 end devices).</summary>
      [Newtonsoft.Json.JsonProperty("join_eui", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public byte[] Join_eui { get; set; }
    
        /// <summary>The LoRaWAN DevAddr.</summary>
        [Newtonsoft.Json.JsonProperty("dev_addr", Required = Newtonsoft.Json.Required.Default, NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore)]
        public byte[] Dev_addr { get; set; }
}

I also had to remove the BitConverter.ToString call

foreach (V3EndDevice device in endDevices.End_devices)
{
   if (DeviceAzureEnabled(device))
   {
      _logger.LogInformation("Config-ApplicationID:{0} DeviceID:{1} Device EUI:{2}", device.Ids.Application_ids.Application_id, device.Ids.Device_id, device.Ids.Dev_eui);

      tasks.Add(DeviceRegistration(device.Ids.Application_ids.Application_id, device.Ids.Device_id, _programSettings.ResolveDeviceModelId(device.Ids.Application_ids.Application_id, device.Attributes), stoppingToken));
   }
}

Now the DeviceEUI values are displayed correctly and searching for EndDevices in Azure Application Insights is easier

TTI V3 Connector application running as a console application showing correct DeviceEUIs

Modifying the nSwag generated classes is a really nasty way of fixing the problem but I think this approach is okay as it’s only one field and any other solution I could find was significantly more complex.

TTI V3 Gateway provisioning Dragino LHT65 Uplink

This very long post is about how to connect a Dragino LHT65 Temperature and Humidity sensor to Azure IoT Central using my TTI/TTN V3Azure IoT Connector and the Digital Twin Definition Language (DTDL).

Dragino LHT65 temperature and Humidity sensor

The first step was to add an application(dragino-lht65) in my The Things Industries(TTI) tenant

TTI/TTN application for my Dragino LHT65 devices
Adding devMobile as a collaborator on the new application
TTI Application API Key configuration

The new Application API Key used by the MQTTnet managed client only needs to have write downlink and read uplink traffic enabled.

FTDI Adapter and modified LHT64 cable

So I could reliably connect to my LHT65 devices to configure them I modified a programming cable so I could use it with a spare FTDI adaptor without jumper wires. Todo this I used a small jewelers screwdriver to “pop” out the VCC cable and move the transmit data line.

After entering the device password and checking the firmware version I used the AT+CFG command to display the device settings

AT+CFG: Print all configurations

[334428]***** UpLinkCounter= 0 *****
[334430]TX on freq 923200000 Hz at DR 2
[334804]txDone
[339807]RX on freq 923200000 Hz at DR 2
[339868]rxTimeOut
[340807]RX on freq 923200000 Hz at DR 2
[340868]rxTimeOut

Correct Password

Stop Tx events,Please wait for all configurations to print
Printf all config...
AT+DEUI=a8 .. .. .. .. .. .. d6
AT+DADDR=01......D6

AT+APPKEY=9d .. .. .. .. .. .. .. .. .. .. .. .. .. .. 2e
AT+NWKSKEY=f6 .. .. .. .. .. .. .. .. .. .. .. .. .. .. 69
AT+APPSKEY=4c 35 .. .. .. .. .. .. .. .. .. .. .. .. .. 3d
AT+APPEUI=a0 .. .. .. .. .. .. 00
AT+ADR=1
AT+TXP=0
AT+DR=0
AT+DCS=0
AT+PNM=1
AT+RX2FQ=923200000
AT+RX2DR=2
AT+RX1DL=1000
AT+RX2DL=2000
AT+JN1DL=5000
AT+JN2DL=6000
AT+NJM=1
AT+NWKID=00 00 00 00
AT+FCU=0
AT+FCD=0
AT+CLASS=A
AT+NJS=0
AT+RECVB=0:
AT+RECV=0:
AT+VER=v1.7 AS923

AT+CFM=0
AT+CFS=0
AT+SNR=0
AT+RSSI=0
AT+TDC=1200000
AT+PORT=2
AT+PWORD=123456
AT+CHS=0
AT+DATE=21/3/26 07:49:15
AT+SLEEP=0
AT+EXT=4,2
AT+RTP=20
AT+BAT=3120
AT+WMOD=0
AT+ARTEMP=-40,125
AT+CITEMP=1
Start Tx events OK


[399287]***** UpLinkCounter= 0 *****

[399289]TX on freq 923400000 Hz at DR 2

[399663]txDone

[404666]RX on freq 923400000 Hz at DR 2

[404726]rxTimeOut

[405666]RX on freq 923200000 Hz at DR 2

[405726]rxTimeOut

I copied the AppEUI and DevEUI for use on the TI Dragino LHT65 Register end device form provided by the TTI/TTN.

TTYI/TTN Dragino LHT65 Register end device

The Dragino LHT65 uses the DeviceEUI as the DeviceID which meant I had todo more redaction in my TTI/TTN and Azure Application Insights screen captures. The rules around the re-use of EndDevice ID were a pain in the arse(PITA) in my development focused tenant.

Dragino LHT 65 Device uplink payload formatter

The connector supports both uplink and downlink messages with JSON encoded payloads. The Dragino LHT65 has a vendor supplied formatter which is automatically configured when an EndDevice is created. The EndDevice formatter configuration can also be overridden at the Application level in the app.settings.json file.

Device Live Data Uplink Data Payload

Once an EndDevice is configured in TTI/TTN I usually use the “Live data Uplink Payload” to work out the decoded payload JSON property names and data types.

LHT65 Uplink only Azure IoT Central Device Template
LHT65 Device Template View Identity

For Azure IoT Central “automagic” provisioning the DTDLModelId has to be copied from the Azure IoT Central Template into the TTI/TTN EndDevice or app.settings.json file application configuration.

LHT65 Device Template copy DTDL @ID
TTI EndDevice configuring the DTDLV2 @ID at the device level

Configuring the DTDLV2 @ID at the TTI application level in the app.settings.json file

{
  "Logging": {
    "LogLevel": {
      "Default": "Debug",
      "Microsoft": "Debug",
      "Microsoft.Hosting.Lifetime": "Debug"
    },
    "ApplicationInsights": {
      "LogLevel": {
        "Default": "Debug"
      }
    }
  },

  "ProgramSettings": {
    "Applications": {
      "application1": {
        "AzureSettings": {
          "DeviceProvisioningServiceSettings": {
            "IdScope": "0ne...DD9",
            "GroupEnrollmentKey": "eFR...w=="
          }
        },
        "DTDLModelId": "dtmi:ttnv3connectorclient:FezduinoWisnodeV14x8;4",
        "MQTTAccessKey": "NNSXS.HCY...RYQ",
        "DeviceIntegrationDefault": false,
        "MethodSettings": {
          "Reboot": {
            "Port": 21,
            "Confirmed": true,
            "Priority": "normal",
            "Queue": "push"
          },
          "value_0": {
            "Port": 30,
            "Confirmed": true,
            "Priority": "normal",
            "Queue": "push"
          },
          "value_1": {
            "Port": 30,
            "Confirmed": true,
            "Priority": "normal",
            "Queue": "push"
          },
          "TemperatureOOBAlertMinimumAndMaximum": {
            "Port": 30,
            "Confirmed": true,
            "Priority": "normal",
            "Queue": "push"
          }
        }
      },
      "seeeduinolorawan": {
        "AzureSettings": {
          "DeviceProvisioningServiceSettings": {
            "IdScope": "0ne...DD9",
            "GroupEnrollmentKey": "AtN...g=="
          },
        },
        "DTDLModelId": "dtmi:ttnv3connectorclient:SeeeduinoLoRaWAN4cz;1",
        "MQTTAccessKey": "NNSXS.V44...42A",
        "DeviceIntegrationDefault": true,
        "DevicePageSize": 10
      },
      "dragino-lht65": {
        "AzureSettings": {
          "DeviceProvisioningServiceSettings": {
            "IdScope": "0ne...DD9",
            "GroupEnrollmentKey": "SLB...w=="
          }
        },
        "DTDLModelId": "dtmi:ttnv3connectorclient:DraginoLHT656w6;1",
        "MQTTAccessKey": "NNSXS.RIJ...NZQ",
        "DeviceIntegrationDefault": true,
        "DevicePageSize": 10
      }
    },
    "TheThingsIndustries": {
      "MqttServerName": "eu1.cloud.thethings.industries",
      "MqttClientId": "MQTTClient",
      "MqttAutoReconnectDelay": "00:00:05",
      "Tenant": "...-test",
      "ApiBaseUrl": "https://...-test.eu1.cloud.thethings.industries/api/v3",
      "ApiKey": "NNSXS.NR7...ZSA",
      "Collaborator": "devmobile",
      "DevicePageSize": 10,
      "DeviceIntegrationDefault": true
    }
  }
}

The Azure Device Provisioning Service(DPS) is configured at the TTI application level in the app.settings.json file. The IDScope and one of the Primary or Secondary Shared Access Signature(SAS) keys should be copied into DeviceProvisioningServiceSettings of an Application in the app.settings.json file. I usually set the “Automatically connect devices in this group” flag as part of the “automagic” provisioning process.

Azure IoT Central Group Enrollment Key
Then device templates need to be mapped to an Enrollment Group then Device Group.

For testing the connector application can be run locally with diagnostic information displayed in the application console window as it “automagically’ provisions devices and uploads telemetry data.

Connector application Diagnostics
Azure IoT Central Device list before my LHT65 device is “automagically” provisioned
Azure IoT Central Device list after my LHT65 device is “automagically” provisioned

One a device has been provisioned I check on the raw data display that all the fields I configured have been mapped correctly.

Azure IoT Central raw data display

I then created a dashboard to display the telemetry data from the LHT65 sensors.

Azure IoT Central dashboard displaying LHT65 temperature, humidity and battery voltage graphs.

The dashboard also has a few KPI displays which highlighted an issue which occurs a couple of times a month with the LHT65 onboard temperature sensor values (327.7°). I have connected Dragino technical support and have also been unable to find a way to remove the current an/or filter out future aberrant values.

Azure Application Insights logging

I also noticed that the formatting of the DeviceEUI values in the Application Insights logging was incorrect after trying to search for one of my Seeedstudio LoRaWAN device with its DeviceEUI.

TTN V3 Gateway Downlink Broken

While adding Azure Device Provisioning Service (DPS) support to my The Things Industries(TTI)/The Things Network(TTN) Azure IoT Hub/Azure IoT Central Connector I broke Cloud to Device(C2D)/Downlink messaging. I had copied the Advanced Message Queuing Protocol(AMQP) connection pooling configuration code from my The Things Network Integration assuming it worked.

return DeviceClient.CreateFromConnectionString(connectionString, deviceId,
	new ITransportSettings[]
	{
		new AmqpTransportSettings(TransportType.Amqp_Tcp_Only)
		{
			PrefetchCount = 0,
			AmqpConnectionPoolSettings = new AmqpConnectionPoolSettings()
			{
				Pooling = true,
			}
		}
	});

I hadn’t noticed this issue in my Azure IoT The Things Network Integration because I hadn’t built support for C2D messaging. After some trial and error I figured out the issue was the PrefetchCount initialisation.

return DeviceClient.CreateFromConnectionString(connectionString, deviceId,
	new ITransportSettings[]
	{
		new AmqpTransportSettings(TransportType.Amqp_Tcp_Only)
		{
			AmqpConnectionPoolSettings = new AmqpConnectionPoolSettings()
			{
				Pooling = true,
			}
		}
	});

From the Azure Service Bus (I couldn’t find any specifically Azure IoT Hub ) documentation

Even though the Service Bus APIs do not directly expose such an option today, a lower-level AMQP protocol client can use the link-credit model to turn the “pull-style” interaction of issuing one unit of credit for each receive request into a “push-style” model by issuing a large number of link credits and then receive messages as they become available without any further interaction. Push is supported through the MessagingFactory.PrefetchCount or MessageReceiver.PrefetchCount property settings. When they are non-zero, the AMQP client uses it as the link credit.

n this context, it’s important to understand that the clock for the expiration of the lock on the message inside the entity starts when the message is taken from the entity, not when the message is put on the wire. Whenever the client indicates readiness to receive messages by issuing link credit, it is therefore expected to be actively pulling messages across the network and be ready to handle them. Otherwise the message lock may have expired before the message is even delivered. The use of link-credit flow control should directly reflect the immediate readiness to deal with available messages dispatched to the receiver.

In the Azure IoT Hub SDK the prefetch count is set to 50 (around line 57) and throws an exception if less that zero (around line 90) and there is some information about tuning the prefetch value for Azure Service Bus.

The best explanation I count find was Github issue which was a query “What exactly does the PrefetchCount property control?”

“You are correct, the pre-fetch count is used to set the link credit over AMQP. What this signifies is the max. no. of messages that can be “in-flight” from the service to the client, at any given time. (This value defaults to 50 for the IoT Hub .NET client).
The client specifies its link-credit, that the service must respect. In simplest terms, any time the service sends a message to the client, it decrements the link credit, and will continue sending messages until linkCredit > 0. Once the client acknowledges the message, it will increment the link credit.”

In summary if Prefetch count is set to zero on startup in my application no messages will be sent to the client….

TTN V3 Gateway Azure Configuration Simplication

To reduce complexity the initial version of the V3 TTI gateway didn’t support the Azure Device Provisioning Service(DPS). In preparation for this I had included DeviceProvisioningServiceSettings object in both the Application and AzureSettingsDefault sections.

After trialing a couple of different approaches I have removed the AzureSettingsDefault. If an application has a connectionstring configured that is used, if there is not one then the DPS configuration is used, if there are neither currently the application logs an error. In the future I will look at adding a configuration option to make the application optionally shutdown

{
  ...
  "ProgramSettings": {
    "Applications": {
      "application1": {
        "AzureSettings": {
          "IoTHubConnectionString": "HostName=TT...n1.azure-devices.net;SharedAccessKeyName=device;SharedAccessKey=Am...M=",
          "DeviceProvisioningServiceSettings": {
            "IdScope": "0n...3B",
            "GroupEnrollmentKey": "Kl...Y="
          }
        },
        "MQTTAccessKey": "NNSXS.HC...YQ",
        "DeviceIntegrationDefault": false,
        "DevicePageSize": 10
      },
      "seeeduinolorawan": {
        "AzureSettings": {
          "IoTHubConnectionString": "HostName=TT...n2.azure-devices.net;SharedAccessKeyName=device;SharedAccessKey=D2q...L8=",
          "DeviceProvisioningServiceSettings": {
            "IdScope": "0n...3B",
            "GroupEnrollmentKey": "Kl...Y="
          }
        },
        "MQTTAccessKey": "NNSXS.V44...42A",
        "DeviceIntegrationDefault": true,
        "DevicePageSize": 10
      }
    },

    "TheThingsIndustries": {
      "MqttServerName": "eu1.cloud.thethings.industries",
      "MqttClientId": "MQTTClient",
      "MqttAutoReconnectDelay": "00:00:05",
      "Tenant": "br...st",
      "ApiBaseUrl": "https://br..st.eu1.cloud.thethings.industries/api/v3",
      "ApiKey": "NNSXS.NR...SA",
      "Collaborator": "de...le",
      "DevicePageSize": 10,
      "DeviceIntegrationDefault": true
    }
  }
}

The implementation of failing back from application to default settings wasn’t easy to implement, explain or document.

Downlink messages NahYeah

While running my The Things IndustriesTTI) gateway I noticed an exception in the logs every so often

Exception of type 'Microsoft.Azure.Devices.Client.Exceptions.DeviceMessageLockLostException' was thrown.

My client subscribes to Message Queue Telemetry Transport Topics(MQTT) (using MQTTNet) for each TTI Application and establishes a connection (using an Azure DeviceClient) for each TTI Device to an Azure IoT Hub(s).

  • v3/{application id}@{tenant id}/devices/{device id}/up
  • v3/{application id}@{tenant id}/devices/{device id}/down/queued
  • v3/{application id}@{tenant id}/devices/{device id}/down/sent
  • v3/{application id}@{tenant id}/devices/{device id}/down/ack
  • v3/{application id}@{tenant id}/devices/{device id}/down/nack
  • v3/{application id}@{tenant id}/devices/{device id}/down/failed

The application subscribes to the queued, ack, nack, and failed topics so the progress of a downlink message can be monitored. For downlink messages the correlation_id “az:LockToken:” contains the message.LockToken so that they can be Abandoned, Completed or Rejected in the MQTT receive messageHandler.

Below is the logging from my application for an odd sequence of messages

*****Nothing much happening for a couple of hours the .'s represent approx 1 second. Wisnode 4 sends roughly every 5 minues

.....................................................................................................................................................................................................................................................................................................................
03:36:08 TTN Uplink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 Port: 5
.....................................................................................................................................................................................................................................................................................................................
03:41:18 TTN Uplink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 Port: 5
...........................................................................
03:42:34 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: 57ea0fad-b6b3-492e-b194-10c4ff3e53cb
 Body: vu8=

*****I then started sending 5 messages to Wisnode 5 same payload vu8=, port 71 thru 75 

***** 71 Queued
03:42:34 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"}},
	"correlation_ids":[
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H"],
	"downlink_queued":{"f_port":71,"frm_payload":"vu8=","confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H"]}}
...
03:42:37 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: e2fef28c-fb1f-42cd-bb40-3ad8e6051da9
 Body: vu8=
.

***** 72 Queued
03:42:38 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"}},
	"correlation_ids":[
"az:LockToken:e2fef28c-fb1f-42cd-bb40-3ad8e6051da9",
"as:downlink:01EXX9B4RGSCJ4BN21GHPM85W5"],
	"downlink_queued":{"f_port":72,"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:e2fef28c-fb1f-42cd-bb40-3ad8e6051da9",
"as:downlink:01EXX9B4RGSCJ4BN21GHPM85W5"]}}
...
03:42:41 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: 70d61d71-9b24-44d2-b54b-7cc08da4d072
 Body: vu8=

***** 73 Queued
03:42:41 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"}},
	"correlation_ids":[
"az:LockToken:70d61d71-9b24-44d2-b54b-7cc08da4d072","as:downlink:01EXX9B800WF7FEP56J3EZ3M8A"],
	"downlink_queued":{"f_port":73,"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:70d61d71-9b24-44d2-b54b-7cc08da4d072",
"as:downlink:01EXX9B800WF7FEP56J3EZ3M8A"]}}
...

***** 74 Queued
03:42:45 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: 12537728-de4a-4489-ace5-92923e49b8e4
 Body: vu8=
.
03:42:45 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"}},
	"correlation_ids":[
"az:LockToken:12537728-de4a-4489-ace5-92923e49b8e4",
"as:downlink:01EXX9BBWA2YNCN2DFE5FC3BP3"],
	"downlink_queued":{
"f_port":74,"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:12537728-de4a-4489-ace5-92923e49b8e4",
"as:downlink:01EXX9BBWA2YNCN2DFE5FC3BP3"]}}
...

***** 75 Queued
03:42:48 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: 388efc11-4514-406e-8147-9109289095f4
 Body: vu8=

03:42:49 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"}},
	"correlation_ids":[
"az:LockToken:388efc11-4514-406e-8147-9109289095f4",
"as:downlink:01EXX9BFCM2G51EPYNWGDWPS0N"],
	"downlink_queued":{"f_port":75,"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:388efc11-4514-406e-8147-9109289095f4",
"as:downlink:01EXX9BFCM2G51EPYNWGDWPS0N"]}}

***** Waiting for Wisniode
..........................................................................................................................................................................
03:47:18 TTN Uplink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 Port: 5

***** Waiting for Wisniode again, I think might have been such a long delay becuase TTI didn't get
..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
***** 71 Nack'd
03:56:52 Nack: v3/application1@tenant1/devices/wisnodetest04/down/nack
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"},
	"dev_eui":"60C5A8FFFE781691","join_eui":"70B3D57ED0000000","dev_addr":"26083BE1"},
	"correlation_ids":[
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H",
"as:up:01EXXA572VHN7X7G5KFTHBQPNG",
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"gs:conn:01EXRPTTFGFNTRGH7V8FTC3R0S",
"gs:up:host:01EXRPTTFTEXBNV87KZFYFWP5V",
"gs:uplink:01EXXA56VPK14XG5S8JB9Q0V0X",
"ns:uplink:01EXXA56VYCHGGPPN1K77REMNM",
"rpc:/ttn.lorawan.v3.GsNs/HandleUplink:01EXXA56VRG6811HRCF803VJ34"],
	"received_at":"2021-02-07T03:56:53.211893610Z",
	"downlink_nack":{
"session_key_id":"AXd6GPmneD3dKVoArcS36g==",
"f_port":71,"f_cnt":35,
"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H"]}}

 Found az:LockToken:

03:56:52 TTN Uplink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 Port: 5

03:56:52 Azure IoT Hub downlink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 LockToken: 856f5a9b-bc37-435c-8de9-19d2213999f8
 Body: vu8=

03:56:53 Queued: v3/application1@tenant1/devices/wisnodetest04/down/queued
 payload: {
"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"},
	"correlation_ids":[
"az:LockToken:856f5a9b-bc37-435c-8de9-19d2213999f8",
"as:downlink:01EXXA57JJWWYEDX3Z55TNSTP5"],
	"downlink_queued":{"f_port":71,
"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":
["az:LockToken:856f5a9b-bc37-435c-8de9-19d2213999f8",
"as:downlink:01EXXA57JJWWYEDX3Z55TNSTP5"]}}

......
***** 71 Ack'd
03:56:58 Ack: v3/application1@tenant1/devices/wisnodetest04/down/ack
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"},
	"dev_eui":"60C5A8FFFE781691","join_eui":"70B3D57ED0000000","dev_addr":"26083BE1"},
	"correlation_ids":[
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H",
"as:up:01EXXA5D45E77S19TXEV1E4GAJ",
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"gs:conn:01EXRPTTFGFNTRGH7V8FTC3R0S",
"gs:up:host:01EXRPTTFTEXBNV87KZFYFWP5V",
"gs:uplink:01EXXA5CV73THH2RKEAC2T9MDP",
"ns:uplink:01EXXA5CVDCWPFBTXGGGB3T02W",
"rpc:/ttn.lorawan.v3.GsNs/HandleUplink:01EXXA5CVDEXDFBPYXC0J01Q3E"],
	"received_at":"2021-02-07T03:56:59.397330003Z",
	"downlink_ack":{
"session_key_id":"AXd6GPmneD3dKVoArcS36g==",
"f_port":71,"f_cnt":36,"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL",
	"correlation_ids":[
"az:LockToken:57ea0fad-b6b3-492e-b194-10c4ff3e53cb",
"as:downlink:01EXX9B1CA4DB68PKCDAK4SS4H"]}}

 Found az:LockToken:
Exception of type 'Microsoft.Azure.Devices.Client.Exceptions.DeviceMessageLockLostException' was thrown.

03:56:59 TTN Uplink message
 ApplicationID: application1
 DeviceID: wisnodetest04
 Port: 0
......
03:57:04 Ack: v3/application1@tenant1/devices/wisnodetest04/down/ack
 payload: {"end_device_ids":{"device_id":"wisnodetest04","application_ids":{"application_id":"application1"},
"dev_eui":"60C5A8FFFE781691","join_eui":"70B3D57ED0000000","dev_addr":"26083BE1"},
"correlation_ids":[
"as:downlink:01EXX9B4RGSCJ4BN21GHPM85W5",
"as:up:01EXXA5K2FWGP9DGD7THWZ8HNR",
"az:LockToken:e2fef28c-fb1f-42cd-bb40-3ad8e6051da9",
"gs:conn:01EXRPTTFGFNTRGH7V8FTC3R0S",
"gs:up:host:01EXRPTTFTEXBNV87KZFYFWP5V",
"gs:uplink:01EXXA5JVDR102TKCWQ77P4YYF",
"ns:uplink:01EXXA5JVGNGMZN33FNT47G6PF",
"rpc:/ttn.lorawan.v3.GsNs/HandleUplink:01EXXA5JVGJFFQVEWX2M1XSFKK"],
"received_at":"2021-02-07T03:57:05.487910418Z","downlink_ack":{"session_key_id":"AXd6GPmneD3dKVoArcS36g==",
"f_port":72,"f_cnt":37,
"frm_payload":"vu8=",
"confirmed":true,"priority":"NORMAL","correlation_ids":
["az:LockToken:e2fef28c-fb1f-42cd-bb40-3ad8e6051da9","as:downlink:01EXX9B4RGSCJ4BN21GHPM85W5"]}}

The sequence of messages is a bit odd, in the Azure DeviceClient ReceiveMessageHandler a downlink message is published, then a queued message is received, then a nak and finally an ack, The exception was because my client was trying to Complete the delivery of a message that had already been Abandoned.

Application Insights & Configuration

As part of my The Things IndustriesTTI) Integration my current approach is to use an Azure web job and configure the Azure App Service host so it doesn’t get shutdown after a period of inactivity. This so my application won’t have to repeatedly use the TTI API to request the Application and Device configuration information to reload the cache (still not certain if this is going to be implemented with a ConcurrentDictionary or ObjectCache).

namespace devMobile.TheThingsNetwork.WorkerService
{
   using System.Collections.Generic;

   public class AzureDeviceProvisiongServiceSettings
   {
      public string IdScope { get; set; }
      public string GroupEnrollmentKey { get; set; }
   }

   public class AzureSettings
   {
      public string IoTHubConnectionString { get; set; }
      public AzureDeviceProvisiongServiceSettings DeviceProvisioningServiceSettings { get; set; }
   }

   public class ApplicationSetting
   {
      public AzureSettings AzureSettings { get; set; }

      public string MQTTAccessKey { get; set; }

      public byte? ApplicationPageSize { get; set; }

      public bool? DeviceIntegrationDefault { get; set; }
      public byte? DevicePageSize { get; set; }
   }

   public class TheThingsIndustries
   {
      public string MqttServerName { get; set; }
      public string MqttClientName { get; set; }

      public string Tennant { get; set; }
      public string ApiBaseUrl { get; set; }
      public string ApiKey { get; set; }

      public bool ApplicationIntegrationDefault { get; set; }
      public byte ApplicationPageSize { get; set; }

      public bool DeviceIntegrationDefault { get; set; }
      public byte DevicePageSize { get; set; }
   }

   public class ProgramSettings
   {
      public TheThingsIndustries TheThingsIndustries { get; set; }

      public AzureSettings AzureSettingsDefault { get; set; }

      public Dictionary<string, ApplicationSetting> Applications { get; set; }
   }
}

The amount of configuration required to support multiple TTI Applications containing many Devices is also starting to get out of hand.

I need to subscribe to a Message Queue Telemetry Transport Topics(MQTT using MQTTNet) for each Application and establish a connection (using an Azure DeviceClient) for each TTI Device to the configured Azure IoT Hub(s).

  • v3/{application id}@{tenant id}/devices/{device id}/up
  • v3/{application id}@{tenant id}/devices/{device id}/down/queued
  • v3/{application id}@{tenant id}/devices/{device id}/down/sent
  • v3/{application id}@{tenant id}/devices/{device id}/down/ack
  • v3/{application id}@{tenant id}/devices/{device id}/down/nack
  • v3/{application id}@{tenant id}/devices/{device id}/down/failed

The Azure DeviceClient has to be configured and OpenAsync called just before/after subscribing to the TTI Application /up topic so the SendEventAsync method can be called to send messages to the configured Azure IoT Hub(s). For downlink messages the SetReceiveMessageHandler method will need to be called just before/after subscribing to ../down/queued, ../down/sent,../down/ack,…/down/nack and ,…/down/failed downlink topics.

The ordering of downloading the Application and Device configuration so downlink messages can be sent and uplink message received as soon as possible (so no messages are lost) is important. I have considered making the downlink process multi-threaded so API calls are made concurrently but I’m not certain the additional complexity would be worth it, especially in initial versions.

I’m also currently not certain about how to register my program for Application and Device registry changes so it doesn’t have to be restarted when configuration changes. I have also considered reverting to an HTTP Integration so that I could use Azure Storage queues to buffer uplink and downlink messages. This may also introduce ordering issues when multiple threads are created for Azure Queue Trigger functions to process a message backlog.

For debugging the application and monitoring in production I was planning on using the Apache Log4Net library but now I’m not certain the additional configuration complexity and dependencies are worth it. The built in Microsoft.Extensions.Logging library with Azure Application Insights integration looks like a “light weight” alternative with sufficient functionality .

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
   while (!stoppingToken.IsCancellationRequested)
   {
      _logger.LogDebug("Debug worker running at: {time}", DateTimeOffset.Now);
      _logger.LogInformation("Info worker running at: {time}", DateTimeOffset.Now);
      _logger.LogWarning("Warning worker running at: {time}", DateTimeOffset.Now);
      _logger.LogError("Error running at: {time}", DateTimeOffset.Now);

      using (_logger.BeginScope("TheThingsIndustries configuration"))
      {
         _logger.LogInformation("Tennant: {0}", _programSettings.TheThingsIndustries.Tennant);
         _logger.LogInformation("ApiBaseUrl: {0}", _programSettings.TheThingsIndustries.ApiBaseUrl);
         _logger.LogInformation("ApiKey: {0}", _programSettings.TheThingsIndustries.ApiKey);

         _logger.LogInformation("ApplicationPageSize: {0}", _programSettings.TheThingsIndustries.ApplicationPageSize);
         _logger.LogInformation("DevicePageSize: {0}", _programSettings.TheThingsIndustries.DevicePageSize);

         _logger.LogInformation("ApplicationIntegrationDefault: {0}", _programSettings.TheThingsIndustries.ApplicationIntegrationDefault);
         _logger.LogInformation("DeviceIntegrationDefault: {0}", _programSettings.TheThingsIndustries.DeviceIntegrationDefault);

         _logger.LogInformation("MQTTServerName: {0}", _programSettings.TheThingsIndustries.MqttServerName);
         _logger.LogInformation("MQTTClientName: {0}", _programSettings.TheThingsIndustries.MqttClientName);
      }

      using (_logger.BeginScope("Azure default configuration"))
      {
         if (_programSettings.AzureSettingsDefault.IoTHubConnectionString != null)
         {
            _logger.LogInformation("AzureSettingsDefault.IoTHubConnectionString: {0}", _programSettings.AzureSettingsDefault.IoTHubConnectionString);
         }

         if (_programSettings.AzureSettingsDefault.DeviceProvisioningServiceSettings != null)
         {
            _logger.LogInformation("AzureSettings.DeviceProvisioningServiceSettings.IdScope: {0}", _programSettings.AzureSettingsDefault.DeviceProvisioningServiceSettings.IdScope);
            _logger.LogInformation("AzureSettings.DeviceProvisioningServiceSettings.GroupEnrollmentKey: {0}", _programSettings.AzureSettingsDefault.DeviceProvisioningServiceSettings.GroupEnrollmentKey);
         }
      }
    
      foreach (var application in _programSettings.Applications)
      {
         using (_logger.BeginScope(new[] { new KeyValuePair<string, object>("Application", application.Key)}))
         {
            _logger.LogInformation("MQTTAccessKey: {0} ", application.Value.MQTTAccessKey);

            if (application.Value.ApplicationPageSize.HasValue)
            {
               _logger.LogInformation("ApplicationPageSize: {0} ", application.Value.ApplicationPageSize.Value);
            }

            if (application.Value.DeviceIntegrationDefault.HasValue)
            {
               _logger.LogInformation("DeviceIntegation: {0} ", application.Value.DeviceIntegrationDefault.Value);
            }

            if (application.Value.DevicePageSize.HasValue)
            {
               _logger.LogInformation("DevicePageSize: {0} ", application.Value.DevicePageSize.Value);
            }

            if (application.Value.AzureSettings.IoTHubConnectionString != null)
            {
               _logger.LogInformation("AzureSettings.IoTHubConnectionString: {0} ", application.Value.AzureSettings.IoTHubConnectionString);
            }

            if (application.Value.AzureSettings.DeviceProvisioningServiceSettings != null)
            {
               _logger.LogInformation("AzureSettings.DeviceProvisioningServiceSettings.IdScope: {0} ", application.Value.AzureSettings.DeviceProvisioningServiceSettings.IdScope);
               _logger.LogInformation("AzureSettings.DeviceProvisioningServiceSettings.GroupEnrollmentKey: {0} ", application.Value.AzureSettings.DeviceProvisioningServiceSettings.GroupEnrollmentKey);
            }
         }
      }

      await Task.Delay(300000, stoppingToken);
   }
}

The logging information formatting is sufficiently readable when running locally

Extensive use of the BeginScope method to include additional meta-data on logged records should make debugging easier.

This long post is to explain some of my design decisions and which ones are still to be decided