Enable stateful mode for stateless built-in ServiceBus comnector

Question

Enable stateful mode for stateless built-in ServiceBus comnector

George Cao 20

hi team,

Our integration using Logic App Standard and Azure Service Bus intermittently suffers from session loss during scale-in events. After reading the recommended scale-out config in this MS article https://learn.microsoft.com/en-us/azure/connectors/enable-stateful-affinity-built-in-connectors, I am a little concerned about the recommended approach. If I understand it correctly, it is suggesting to almost effectively disable the whole scale-out feature. This totally defeats the purpose of the scale-out handling, while users will be billed for all idle (Always Ready) instances.

Could you confirm if my understanding is correct? and do you have any alternatives?

Thanks

George

Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-13T07:03:33.3733333+00:00
Hello George Cao,

Thanks for reaching out, as per your description can you please tell us where you found this statement "it is suggesting to almost effectively disable the whole scale-out feature"?As per your concern please refer the below steps,

Resource scale-in events might cause the loss of context for built-in connectors with stateful mode enabled. To prevent this potential loss before such events can happen, fix the number of instances available for your logic app resource. This way, no scale-in events can happen to cause this potential context loss.

On your logic app resource menu, under Settings, select Scale out (App Service plan).

On the Scale out (App Service plan) page, in the App Scale out section, follow these steps:

Set Enforce Scale Out Limit to Yes, which shows the Maximum Scale Out Limit property.

Set Always Ready Instances to the same number as Maximum Scale Out Limit and Maximum Burst, which appears in the Plan Scale out section, for example:

When you're done, on the Scale out toolbar, select Save.
George Cao 20 Reputation points

2025-06-15T12:27:20.7333333+00:00

hi Loknathsatyasaivarma,

The suggested configuration is to "fix the number of instances available for your Logic App resource," as stated in the documentation. This approach pre-allocates a set number of "Always Ready Instances" upfront, preventing scale-out events and, consequently, avoiding scale-in events. However, the user will still be billed for all "Always Ready Instances", even when they are idle.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-16T04:41:01.4433333+00:00

Hello George Cao,

Yes, your understanding is correct. The instances are billable when they are set to ALWAYS READY instances, even if they are in an idle state. As per the document. Also to prevent context loss during scale-in, fix your worker instance count by setting 'Always Ready Instances' to the same value as your 'Maximum Scale Out Limit'.
George Cao 20 Reputation points

2025-06-16T06:08:34.3766667+00:00

yes, that's my concern that when Always Ready Instances = Minimum Instances = Maximum Burst, it prevents Logic App from scaling out under load
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-17T12:05:38.71+00:00

Hello George Cao,

Thanks for raising this your understanding is absolutely correct.

When Always Ready Instances = Minimum Instances = Maximum Burst, it effectively disables scale-out. This setup is recommended to preserve session affinity and prevent session loss during scale-in events, especially for Service Bus sessions. However, the trade-off is that all allocated instances remain active and billable, even when idle.

At this time, there’s no built-in way to maintain session reliability and still allow full dynamic scaling in Logic App Standard. As an alternative, some customers choose to isolate session-based workloads or use Durable Functions for more flexible scaling with session support.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-18T16:44:10.9033333+00:00

Hello George Cao,

Just checking in to see if you had a chance to review my previous message. If you have any further concerns, please feel free to share them here.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-19T14:34:43.0733333+00:00

Hello George Cao,

We wanted to follow up on the issue you encountered. Please let us know if it's resolved or if you need further assistance.

Your answer

Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-13T07:03:33.3733333+00:00

Hello George Cao,

Thanks for reaching out, as per your description can you please tell us where you found this statement "it is suggesting to almost effectively disable the whole scale-out feature"?As per your concern please refer the below steps,

Resource scale-in events might cause the loss of context for built-in connectors with stateful mode enabled. To prevent this potential loss before such events can happen, fix the number of instances available for your logic app resource. This way, no scale-in events can happen to cause this potential context loss.

On your logic app resource menu, under Settings, select Scale out (App Service plan).

On the Scale out (App Service plan) page, in the App Scale out section, follow these steps:

Set Enforce Scale Out Limit to Yes, which shows the Maximum Scale Out Limit property.

Set Always Ready Instances to the same number as Maximum Scale Out Limit and Maximum Burst, which appears in the Plan Scale out section, for example:

When you're done, on the Scale out toolbar, select Save.
George Cao 20 Reputation points

2025-06-15T12:27:20.7333333+00:00

hi Loknathsatyasaivarma,

The suggested configuration is to "fix the number of instances available for your Logic App resource," as stated in the documentation. This approach pre-allocates a set number of "Always Ready Instances" upfront, preventing scale-out events and, consequently, avoiding scale-in events. However, the user will still be billed for all "Always Ready Instances", even when they are idle.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-16T04:41:01.4433333+00:00

Hello George Cao,

Yes, your understanding is correct. The instances are billable when they are set to ALWAYS READY instances, even if they are in an idle state. As per the document. Also to prevent context loss during scale-in, fix your worker instance count by setting 'Always Ready Instances' to the same value as your 'Maximum Scale Out Limit'.
George Cao 20 Reputation points

2025-06-16T06:08:34.3766667+00:00

yes, that's my concern that when Always Ready Instances = Minimum Instances = Maximum Burst, it prevents Logic App from scaling out under load
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-17T12:05:38.71+00:00

Hello George Cao,

Thanks for raising this your understanding is absolutely correct.

When Always Ready Instances = Minimum Instances = Maximum Burst, it effectively disables scale-out. This setup is recommended to preserve session affinity and prevent session loss during scale-in events, especially for Service Bus sessions. However, the trade-off is that all allocated instances remain active and billable, even when idle.

At this time, there’s no built-in way to maintain session reliability and still allow full dynamic scaling in Logic App Standard. As an alternative, some customers choose to isolate session-based workloads or use Durable Functions for more flexible scaling with session support.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-18T16:44:10.9033333+00:00

Hello George Cao,

Just checking in to see if you had a chance to review my previous message. If you have any further concerns, please feel free to share them here.
Loknathsatyasaivarma Mahali 2,740 Reputation points Microsoft External Staff Moderator

2025-06-19T14:34:43.0733333+00:00

Hello George Cao,

We wanted to follow up on the issue you encountered. Please let us know if it's resolved or if you need further assistance.

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Enable stateful mode for stateless built-in ServiceBus comnector

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