Reference - IoT Hub quotas and throttling

Quotas and throttling

Each Azure subscription can have at most 50 IoT hubs, and at most 1 Free hub.

Each IoT hub is provisioned with a certain number of units in a specific tier. The tier and number of units determine the maximum daily quota of messages that you can send. The message size used to calculate the daily quota is 0.5 KB for a free tier hub and 4KB for all other tiers. For more information, see Azure IoT Hub Pricing.

The tier also determines the throttling limits that IoT Hub enforces on all operations.

Operation throttles

Operation throttles are rate limitations that are applied in minute ranges, and are intended to prevent abuse. IoT Hub tries to avoid returning errors whenever possible, but starts returning 429 ThrottlingException if the throttle is violated for too long.

At any given time, you can increase quotas or throttle limits by increasing the number of provisioned units in an IoT hub.

The following table shows the enforced throttles. Values refer to an individual hub.

Throttle Free, B1, and S1 B2 and S2 B3 and S3
Identity registry operations (create, retrieve, list, update, delete) 1.67/sec/unit (100/min/unit) 1.67/sec/unit (100/min/unit) 83.33/sec/unit (5000/min/unit)
New device connections (this limit applies to the rate at which new connections are established, not the total number of connections) Higher of 100/sec or 12/sec/unit
For example, two S1 units are 2*12 = 24 new connections/sec, but you have at least 100 new connections/sec across your units. With nine S1 units, you have 108 new connections/sec (9*12) across your units.
120 new connections/sec/unit 6000 new connections/sec/unit
Device-to-cloud sends Higher of 100/sec or 12/sec/unit
For example, two S1 units are 2*12 = 24/sec, but you have at least 100/sec across your units. With nine S1 units, you have 108/sec (9*12) across your units.
120/sec/unit 6000/sec/unit
Cloud-to-device sends1 1.67/sec/unit (100/min/unit) 1.67/sec/unit (100/min/unit) 83.33/sec/unit (5000/min/unit)
Cloud-to-device receives1
(only when device uses HTTPS)
16.67/sec/unit (1000/min/unit) 16.67/sec/unit (1000/min/unit) 833.33/sec/unit (50000/min/unit)
File upload 1.67 file upload notifications/sec/unit (100/min/unit) 1.67 file upload notifications/sec/unit (100/min/unit) 83.33 file upload notifications/sec/unit (5000/min/unit)
Direct methods1 160KB/sec/unit2 480KB/sec/unit2 24MB/sec/unit2
Twin (device and module) reads1 10/sec Higher of 10/sec or 1/sec/unit 50/sec/unit
Twin updates (device and module)1 10/sec Higher of 10/sec or 1/sec/unit 50/sec/unit
Jobs operations1,3
(create, update, list, delete)
1.67/sec/unit (100/min/unit) 1.67/sec/unit (100/min/unit) 83.33/sec/unit (5000/min/unit)
Jobs device operations1
(update twin, invoke direct method)
10/sec Higher of 10/sec or 1/sec/unit 50/sec/unit
Configurations and edge deployments1
(create, update, list, delete)
0.33/sec/unit (20/min/unit) 0.33/sec/unit (20/min/unit) 0.33/sec/unit (20/min/unit)

1This feature is not available in the basic tier of IoT Hub. For more information, see How to choose the right IoT Hub.
2Throttling meter size is 8 KB.
3You can only have one active device import/export job at a time.

The device connections throttle governs the rate at which new device connections can be established with an IoT hub. The device connections throttle does not govern the maximum number of simultaneously connected devices. The device connections rate throttle depends on the number of units that are provisioned for the IoT hub.

For example, if you buy a single S1 unit, you get a throttle of 100 connections per second. Therefore, to connect 100,000 devices, it takes at least 1000 seconds (approximately 16 minutes). However, you can have as many simultaneously connected devices as you have devices registered in your identity registry.

For an in-depth discussion of IoT Hub throttling behavior, see the blog post IoT Hub throttling and you.

Important

Identity registry operations are intended for run-time use in device management and provisioning scenarios. Reading or updating a large number of device identities is supported through import and export jobs.

Other limits

IoT Hub enforces other operational limits:

Operation Limit
File upload URIs 10000 SAS URIs can be out for a storage account at one time.
10 SAS URIs/device can be out at one time.
Jobs1 Job history is retained up to 30 days
Maximum concurrent jobs is 1 (for Free) and S1, 5 (for S2), 10 (for S3).
Additional endpoints Paid SKU hubs may have 10 additional endpoints. Free SKU hubs may have one additional endpoint.
Message routing rules Paid SKU hubs may have 100 routing rules. Free SKU hubs may have five routing rules.
Device-to-cloud messaging Maximum message size 256 KB
Cloud-to-device messaging1 Maximum message size 64 KB. Maximum pending messages for delivery is 50.
Direct method1 Maximum direct method payload size is 128 KB.
Automatic device configurations1 100 configurations per paid SKU hub. 20 configurations per free SKU hub.
Automatic Edge deployments1 20 modules per deployment. 100 deployments per paid SKU hub. 20 deployments per free SKU hub.
Twins1 Maximum size per twin section (tags, desired properties, reported properties) is 8 KB

1This feature is not available in the basic tier of IoT Hub. For more information, see How to choose the right IoT Hub.

Note

Currently, the maximum number of devices you can connect to a single IoT hub is 500,000. If you want to increase this limit, contact Microsoft Support.

Latency

IoT Hub strives to provide low latency for all operations. However, due to network conditions and other unpredictable factors it cannot guarantee a maximum latency. When designing your solution, you should:

  • Avoid making any assumptions about the maximum latency of any IoT Hub operation.
  • Provision your IoT hub in the Azure region closest to your devices.
  • Consider using Azure IoT Edge to perform latency-sensitive operations on the device or on a gateway close to the device.

Multiple IoT Hub units affect throttling as described previously, but do not provide any additional latency benefits or guarantees.

If you see unexpected increases in operation latency, contact Microsoft Support.

Next steps

Other reference topics in this IoT Hub developer guide include: