VNET integration with multiple Azure Functions hosted on two App Service Plans

Cosmin Stirbu 151

Hello,

I am looking for some guidance related to VNET and multiple Azure Functions hosted on two separate App Service Plans.

Initially my setup was the following:

1 VNET with one Subnet. This VNET has peering with another VNET where the database is hosted.
6 Azure Functions hosted on a single App Service Plan - each function is integrated with the VNET / Subnet

Using Terraform I migrated to the following setup:

1 VNET with one Subnet
4 Azure Functions hosted on a new App Service Plan - each function is integrated with the VNET / Subnet
2 Azure Functions hosted on a different new App Service Plan - each function is integrated with the VNET / Subnet

The initial App Service Plan was deleted.

Everything works as expected, however I have two concerns:

The old App Service Plan is referenced on the subnet in serviceAssociationLinks
Based on the documentation (https://learn.microsoft.com/en-us/azure/azure-functions/functions-networking-options) this new setup shouldn't work, so I'm confused if I should make any other changes or not:
- The integration subnet can be used by only one App Service plan.
- You can have only one regional VNet Integration per App Service plan. Multiple apps in the same App Service plan can use the same VNet.

Based on my concerns above, I'd like to understand if my new setup (2 App Service Plans and one VNET / Subnet) is working as expected / document or if it is working accidentally and I should make changes to it.

Thank you,
Cosmin

GitaraniSharma-MSFT 47,686 Reputation points Microsoft Employee

2021-03-19T12:38:28.4+00:00

Hello @Cosmin Stirbu ,

Apologies for the delay in response.

Per the limitations, the integration subnet can be used by only one App Service plan and this holds true. When you try to integrate another App service plan to an already integrated subnet manually, it will not allow such an operation. I'm not sure what happened in the backend when you migrated the setup using Terraform which allowed both App service plans to be integrated with same subnet. In order to investigate what happened in this case, we would need the backend logs and hence if you have a support plan, I request you file a support ticket, else please do let us know, we will try and help you get a one-time free technical support.

Thank you for your cooperation on this matter and I look forward to your reply.

Regards,
Gita
GitaraniSharma-MSFT 47,686 Reputation points Microsoft Employee

2021-03-24T14:25:49.037+00:00

<<<<<<UPDATE>>>>>>

Discussed with @Cosmin Stirbu over private message and below is the update from their end:

They created a dedicated subnet for each of the two App Service plans so they're not really keen into digging deeper to understand why they were able to configure two plans with the same subnet.

Hence, we are closing this issue.

Thanks,
Gita