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planet77-0395 asked GitaraniSharmaMSFT-4262 commented

Lost connection to ACI delegated subnet

Hi All,

We recently had an issue where our application subnet could no longer communicate with the ACI delegated subnet.

Application subnet == private-vm (
ACI subnet == private-aci (

The application was working fine, but we lost access to the ACI subnet for no apparent reason. This caused the app to retry connections to the ACI object which would fail.

Restarting the ACI object didn't resolve the issue, and we observed this problem across two different (but similar) resource groups.

I then made a change to the private-aci subnet and removed the nat gateway. This caused the vnet to reprovision. Once that succeeded, the network connectivity between the two subnets started working.

Running diagnostics on the vnet showed some changes to the delegation service during the reprovisioning process as follows:-

Old == delegations/ACIDelegationService"
New == delegations/Microsoft.ContainerInstance.containerGroups"

Does anyone know whether this would have caused the connectivity issues? If so - why?


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Hello @planet77-0395 ,

It is difficult to rule out the root cause of this described issue without looking into the resource. 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.


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