Ordering of events received from Azure Event Grid (Trigger: When a resource event occurs)

[autopower]

I want to process events in the exact order they were published on an event grid topic. However, Power Automate seems to struggle with this.

When many events are published almost simultaneously to a topic, they get processed randomly. Even though I've set up the flow's trigger with concurrency control and limited it to one parallel execution, it's not processing events sequentially as I hoped.

If a flow instance is in line waiting while another one is running, the waiting instances seem to start randomly. This causes events to be processed out of sequence.

Is this a recognized issue? Is there a way to ensure events are processed in their original order?

[Koen5]

Dear A,

While I do not have the issues you mention (concurrency and order works fine) or a solution to this, maybe I could suggest a way it can still function as intended?

What if you run your initial flow as something which records the event/trigger with some relevant details in a table/list. Then you can run a second flow periodically to read the list and process the relevant flow in the right sequence... I am sure one of the details would determine the sequence. There are plenty of forum entries on how to sort or get the max entry in an array.

There will be some delay in your setup, but should only be a few minutes depending on the setup you choose.

Hope the suggestion helps,

Koen

[autopower]

The docs has this to say wrt ordering (Azure - Managing Event Delivery with Azure Event Grid | Microsoft Learn):

Event Grid treats each event independently. This means that there isn’t a guaranteed order for the events and, in some cases, an event can be delivered more than once. Therefore, it’s the responsibility of the event handler to code defensively and be idempotent. Sending the same event repeatedly should produce the same result. If the ordering of events is a requirement, this should be managed on either the compute side (within the logic of the event handler) or by using another service such as Service Bus or Event Hubs to preserve their order.

So, as you mentioned, if I want to preserve ordering I would need to store the events elsewhere and order them. Will also look into Service Bus and/or Event Hubs (need to investigate if those are supported in Power automate).