How to Set Alert for Message Throttling

Hello John Wong Yek Hon,

Here is your Step-by-Step Guide to Set Alert for Message Throttling in Azure IoT Hub

Step 1: Understand Your IoT Hub Quota

• Go to your IoT Hub in the Azure Portal.
• Navigate to Settings > Pricing and Scale.
• Note your daily message quota based on your SKU and number of units (e.g., S1 = 400,000 messages/day/unit, S2 = 6 million messages/day/unit).

Step 2: Enable Diagnostic Settings

• In the IoT Hub blade, go to Monitoring > Diagnostic settings.
• Create a new diagnostic setting:
  • Select Send to Log Analytics workspace.
    • Choose categories like DeviceTelemetry, Connections, and Operations.
      • Save the configuration.

This enables telemetry and operational logs to be sent to Log Analytics for custom querying and alerting

Step 3: Create a Log Analytics Workspace

• If you don’t already have one:
  • Go to Azure Portal > Create a resource > Log Analytics Workspace.
    • Link this workspace to your IoT Hub via the diagnostic settings.

Step 4: Write a Custom Kusto Query

Use the following Kusto query to calculate daily message usage:

AzureDiagnostics
| where ResourceType == "IOTHUBS"
| where Category == "DeviceTelemetry"
| summarize TotalMessages = count() by bin(TimeGenerated, 1d)
| extend UsagePercent = (TotalMessages * 100.0) / 
| where UsagePercent >= 70

Replace <YourDailyQuota> with your actual quota (e.g., 6000000 for S2 tier with 1 unit).

Step 5: Create an Alert Rule

• Go to Azure Monitor > Alerts > New Alert Rule.
• Set the Scope to your IoT Hub.
• Set the Condition:
  • Use Custom log search.
    • Paste the Kusto query.
      • Set the threshold to trigger when UsagePercent ≥ 70 or 80.
      • Set Action Group:
        • Choose email, SMS, webhook, or automation runbook.
        • Name and save the alert rule.

You can monitor multiple thresholds by creating separate alert rules for 70%, 80%, and 90%.

Step 6: Test Your Alert

• Simulate message traffic using a device or script.
• Monitor the alert dashboard.
• Confirm that alerts trigger when thresholds are crossed.

Reference :

https://learn.microsoft.com/en-us/azure/iot-hub/tutorial-use-metrics-and-diags?wt.mc_id=knowledgesearch_inproduct_azure-cxp-community-insider#set-up-metric-alerts

Hope this helps.
Thank you!

Hi,

Thanks for the comprehensive steps given :)

I found the query require us to provide the total message limit per day. Hence whenever I scale the IoT Hub, I will have to update the query as well. Is there a way to auto retrieve the max total message limit instead of hardcode it in the query?

Hello John Wong Yek Hon,

To answer your query, I would suggest a few workarounds you can consider.
Unfortunately, Azure Monitor and Log Analytics do not currently provide a built-in way to dynamically retrieve the IoT Hub's daily message quota within a Kusto query.

1. Use Azure Resource Graph (Outside Log Analytics)

You can use Azure Resource Graph to query your IoT Hub's SKU and unit count, which determines the quota. This can be automated via scripts or Azure Functions to update your alert logic accordingly.

2. Store Quota as a Parameter

You can store your quota value in a parameter or a configuration file (e.g., Azure App Configuration or Key Vault) and reference it in your alerting logic outside of Kusto. This way, when you scale, you only need to update the config—not the query itself.

3. Use Azure Automation

Set up an Azure Automation Runbook that:

• Queries the IoT Hub's current SKU and unit count via ARM API.
• Calculates the quota.
• Updates the alert rule or sends a notification if usage exceeds a threshold.

4. Manual Update with Notification

If automation isn't feasible, consider setting up a process where scaling the IoT Hub triggers a notification to update the alert query manually. This can be part of your operational checklist.

Hope this helps.
Thank you!