Architectue : Overview
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Azure Function & VNet Integration
It allows the function app to access resources in a VNet without exposing them to the internet. It’s useful for securing outbound traffic from the function app.
Outbound Traffic Control : By integrating the function app (FA) with a VNet, we can control the outbound traffic using a NET gateway. This ensures that all outbound traffic from FA uses specific static public IP addresses --> Control Azure Functions outbound IP with an Azure virtual network NAT gateway | Microsoft Learn
Security : VNet Integration helps in securing FA by allowing it to communicate with resources in VNet privately.
Subnet : We need to deploy a NAT Gateway in a subnet of a VNet. It will be associated with one or more subnets within the VNet to provide outbound connectivity for the resources in those subnets.
No inbound traffic from the internet can pass through a NAT gateway : Azure NAT Gateway frequently asked questions | Microsoft Learn
NSG : While it is not mandatory when deploying a NAT gateway in a subnet, it is highly recommended for enhancing security.