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function app does not connect when deployed to a new environment

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function not working after migration to production environment

Matt Elman 20 Reputation points
2025-12-09T21:50:37.01+00:00

We created an Azure Function App and we want to use VNet integration so it can connect to our SQL servers inside its virtual network. 

We successfully created a UAT version of this (using dev resource group, vnet...) and everything works fine. However, when we created a production version of the Function App it would not connect.

  1. Once we enable VNet Integration, the Function App becomes unreachable externally

    The public endpoint immediately returns “Service Unavailable”. 

    Even simple HTTP triggers (e.g., StartRun) fail to respond.

  1. Disabling VNet Integration, the Function App works, but

    We have to open the SQL port 

    Whitelisting PossibleOutboundIPAddress did not work

  1. UAT version works — Production version does not

    The UAT Function App, running in a different VNet (Tech_Development), works both externally and with SQL.

    When we replicate the same setup in Production, it fails once VNet Integration is enabled

Azure Functions
Azure Functions
An Azure service that provides an event-driven serverless compute platform.

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