The technical requirement states that all outbound traffic from the function apps to the on-premises network must use ExpressRoute circuits . To accomplish this, the Function App hosting plan must support outbound virtual network integration , because the application must send outbound traffic into an Azure virtual network from which routes learned through or directed toward the ExpressRoute gateway can reach the on-premises environment.
Fa1 , which uses the Flex Consumption plan , supports virtual network integration. Microsoft documents that Flex Consumption provides outbound virtual network connectivity and can therefore reach resources accessible through the integrated virtual network. Microsoft Learn
Fa3 , which uses a Dedicated App Service plan , also supports outbound virtual network integration. Microsoft further documents that VNet-integrated Functions can have outbound traffic affected by BGP routes learned from an ExpressRoute gateway , and route tables can direct traffic through that gateway. Microsoft Learn
Fa2 , however, uses the legacy Consumption plan , which does not support outbound virtual network integration. Consequently, it cannot meet the requirement to route its outbound on-premises traffic through ExpressRoute using this architecture. Microsoft Learn
Therefore, only Fa1 and Fa3 support the required networking configuration.
