NotificationAlerting.md

Notification and Alerting

Very often in IoT solutions, it is important to receive notifications whenever some tasks complete or systems reach certain thresholds. Those notifications can trigger business processes, generate automated actions to calibrate or even stop production to avoid bigger failures. As it was already discussed in the Azure Stream Analytics Cloud section, telemetry events labeled as alerts are sent to the alerts event hub and telemetry events where the tag AlternatingBoolean is set to true are sent to the notifications event hub. In this section we will discuss how to handle those events using Logic Apps.

Azure Logic Apps is a cloud service that helps you schedule, automate, and orchestrate tasks, business processes, and workflows when you need to integrate apps, data, systems, and services across enterprises or organizations. Logic Apps simplifies how you design and build scalable solutions for app integration, data integration, system integration, enterprise application integration (EAI), and business-to-business (B2B) communication, whether in the cloud, on premises, or both.

Every logic app workflow has two main components: triggers and actions. Triggers fire when a specific event occurs, or when new available data meets specific requirements. Each time that the trigger fires, the Logic Apps engine creates a logic app instance that runs the actions in the workflow. These actions can also include data conversions and workflow controls, such as conditional statements, switch statements, loops, and branching. In our case, there are two Logic Apps solutions, NotificationsApp and AlertsApp. For both of them the trigger is whenever there are new events in Azure Event Hubs, and the main action is to send a message via Azure Event Grid.

[!NOTE:] Both Logic Apps solutions were created using the latest Azure Logic Apps Tools for Visual Studio, since it provides the same logic app designer view as in the Azure Portal and you can also keep the solution in your code repository. For more details about how to install and use the Azure Logic Apps Tools for Visual Studio, take a look at this document.

Notifications App workflow

In this workflow, whenever new events are available in the notifications Event Hub, certain actions take place to do the following:

• Initialize a variable with the event's content
• Parse the event's content in JSON format using the following schema:

{
  "properties": {
    "AlternatingBoolean": {
      "type": "boolean"
    },
    "ApplicationUri": {
      "type": "string"
    },
    "NodeId": {
      "type": "string"
    },
    "SourceTimestamp": {
      "type": "string"
    },
    "Status": {
      "type": "string"
    }
  },
  "type": "object"
}

• Evaluate whether the property AlternatingBoolean is equal to true. If so:
• Send a message like the one below to an Event Grid topic to be broadcasted to all its subscriptions:

{
  "id": "__connection_device_id__/__application_uri__/__node_id__",
  "subject": "IoT Notification",
  "eventType": "Notification",
  "data": {
    "AlternatingBoolean": true
  },
  "dataVersion": "",
  "metadataVersion": "1",
  "eventTime": "__source_timestamp__",
  "topic": "/subscriptions/__subscription__/resourceGroups/__resource_group__/providers/Microsoft.EventGrid/topics/__event_grid_topic__"
}

If you set up your webhook using Webhook.site like it was suggested during the Pre-requisites, you should see events coming in like this one:

You can take a look at the full Visual Studio solution here.

Alerts App workflow

Similarly to the Notifications workflow, when new events are available in the alerts Event Hub, certain actions take place to do the following:

• Initialize a variable with the event's content
• Parse the event's content in JSON format using the following schema:

{
  "type": "object",
  "properties": {
    "NodeId": {
        "type": "string"
    },
    "ApplicationUri": {
        "type": "string"
    },
    "SourceTimestamp": {
        "type": "string"
    },
    "Tag": {
        "type": "string"
    },
    "Value": {
        "type": "number"
    },
    "IsAlert": {
        "type": "integer"
    },
    "AnomalyScore": {
        "type": "number"
    },
    "ConnectionDeviceId": {
        "type": "string"
    }
  }
}

• Evaluate whether the property IsAlert is equal to 1. If so, then:
• Send a message like the one below to an Event Grid topic to be broadcasted to all its subscriptions:

[
  {
    "id": "__connection_device_id__/__application_uri__/__node_id__",
    "subject": "IoT Notifications",
    "eventType": "Alert",
    "data": {
      "Tag": "__tag__",
      "Value": __value__,
      "Score": __score__
    },
    "dataVersion": "",
    "metadataVersion": "1",
    "eventTime": "__source_timestamp__",
    "topic": "/subscriptions/__subscription__/resourceGroups/__resource_group__/providers/Microsoft.EventGrid/topics/__event_grid_topic__"
  }
]

Once again, you should see events coming in like this one:

You can take a look at the full Visual Studio solution here.

[!NOTE:] The reason why we evaluate the AlternatingBoolean property as a Boolean and the IsAlert property as an integer is because Azure Stream Analytics handles Booleans as bigint. You can find more information about Azure Stream Analytics data types here.