Clarification on Whether Acknowledgment Messages Count Towards Azure IoT Hub Daily Message Quota

Question

Hello Azure Support Team,

I am seeking clarification regarding the Azure IoT Hub's daily message quota, specifically concerning acknowledgment messages.

In our current setup, we utilize cloud-to-device messaging and request delivery acknowledgments for each message sent. We would like to understand whether these acknowledgment messages are counted against our IoT Hub's daily message quota.​learn.microsoft.com

The official documentation outlines the operations that contribute to the daily message quota, such as device-to-cloud telemetry messages and cloud-to-device messages. However, it does not explicitly state whether acknowledgment messages, generated upon setting the 'Ack' property in cloud-to-device messages, are included in this count.​

Could you please confirm if acknowledgment messages are considered part of the daily message quota? Additionally, if they are included, could you provide guidance on how they are measured and any best practices to manage their impact on the quota?

Thank you for your assistance.

Best regards

Answer 1

Hello @Jordan Reyes Leger,

welcome to this moderated Azure community forum.

An Azure IoT Hub is a service where the pricing is based on the expected daily consumption.

This is measured in the 'number of daily messages', starting with 400.000 'messages' per day.

These 'messages' are better known as chunks of 4KB parts of messages.

A 5KB message is counted as 2 chunks of 4KB.

The message consumption is based on both device-to-cloud messaging (eg sending one message or a batch of messages or starting a file upload) and cloud-to-device messaging (eg. direct methods, desired properties, reported properties, cloud messages).

Check the documentation regarding the details of counting messages per way of communication.

The underlying protocol is mostly based on MQTT although customers can also used AMQP (and even HTTP although this is strongly discouraged).

Azure IoT Hub offers an 'at least once' delivery for reliability.

Regarding counting the acknowledgement as messages, for as far as I know, these acknowledgements are part of the underlying protocol so these are not part of the message body of the message being transported by that protocol.

Unsuccessful deliveries will result in a resent so those are expected to be counted too as a message.

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Answer 2

Hello Jordan Reyes Leger,

The daily message quota for an IoT Hub includes several types of operations. Here are the key operations that count towards this quota:

1. Device-to-Cloud Messages: These are messages sent from your IoT devices to the cloud. Each message is metered in 4 KB blocks for paid tiers and 0.5 KB blocks for the free tier
2. Cloud-to-Device Messages: These are messages sent from the cloud to your IoT devices. Similar to device-to-cloud messages, they are metered in 4 KB blocks
3. Device Twin Operations: These include operations such as reading, writing, and updating device twins, which are JSON documents that store device state information
4. Job Operations: These include operations related to managing jobs, such as scheduling and monitoring jobs that update device twins or invoke direct methods on devices

Here in case of acknowledgment messages , they are feedback message verifying status of sent messages from cloud to device , there by consuming some server capacity to verify connection stability. Should be counted as Cloud to Device message. 
You can view the default metrics like cloud device completed, purged etc. from monitor section. In order, to drill down specific count on feedback message, You can draft CLI commands or kusto query to find the number of feedback message in an hour or day.

Kindly refer the below documents :
Reference for Kusto queries - Monitor Azure IoT Hub | Microsoft Learn
Reference for CLI command - az iot hub | Microsoft Learn
Reference for Azure IOT Hub Monitor - Monitor Azure IoT Hub | Microsoft Learn

Hope this helps. Do let us know if you any further queries.

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