How do Azure Functions scale in relation to Event Hubs partitions?

Question

How do Azure Functions scale in relation to Event Hubs partitions?

Wessel Vonk 45

Hi, I'm using Azure Functions with an Event Hub trigger and would like to confirm how scaling and partition assignment works in this integration.

From my understanding:

Only one function instance processes events from a given partition at any one time, to maintain message order, offset integrity, etc.
Therefore, the maximum number of concurrently running function instances is equal to the number of partitions in the Event Hub (each partition is exclusively handled by a single instance at a time).
To increase parallel processing, one has to increase the number of partitions in the Event Hub.

Is that indeed the intended and recommended scaling model?

Thanks in advance!

phemanth 15,320 Reputation points Microsoft External Staff

2025-04-18T06:01:07.79+00:00

@Wessel Vonk Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

2 answers

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phemanth 15,320 Reputation points Microsoft External Staff

2025-04-18T06:01:07.79+00:00

@Wessel Vonk Just checking in to see if the below answer helped. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 1

@Wessel Vonk

You're correct in your understanding of how Azure Functions scale in relation to Event Hubs partitions. Here's a bit more detail to confirm and expand on your points:

Single Instance per Partition: Indeed, only one function instance processes events from a given partition at any one time. This ensures that the order of messages and offset integrity are maintained.

Maximum Concurrent Instances: The maximum number of concurrently running function instances is equal to the number of partitions in the Event Hub. Each partition is handled by a single instance to maintain the integrity of the event stream.

Increasing Parallel Processing: To increase parallel processing, you would need to increase the number of partitions in the Event Hub. This allows more function instances to run concurrently, each processing events from a different partition.

This scaling model is designed to ensure that the processing of events is both efficient and orderly. If you need to handle a higher volume of events, increasing the number of partitions is the recommended approach.

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

phemanth 15,320 Reputation points Microsoft External Staff

2025-04-21T05:36:20.5866667+00:00

@Wessel Vonk Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 2

Sander van de Velde | MVP 36,146 MVP

Hello @Wessel Vonk ,

The answer @phemanth gives is a good starting point.

Keep in mind that the number of Eventhub partitions are set at creation and cannot change anymore afterwards when using Basic or standard tier. Higher tiers can change that number.

There is also a limitation on the number of partitions per eventhub, different per tier.

More information about partitions is found here.

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How do Azure Functions scale in relation to Event Hubs partitions?

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