proxy-deprecation impact on consumption based deployments

Logging a new issue for visibility, with additional detail provided on the existing issue #2306.

We've built a business around consumption-based Azure resources that enable us to contain platform expenses with school-based traffic that is unpredictable, bursty, and idle more often than not.

Discontinuation of proxy support in v4 Functions and the suggested migration to APIM was a concern, but was not at 'house on fire' alarm levels until we actually started the migration this week.

Yes APIM is available on a consumption tier. But we need to secure our function apps from internet access AND need to address issues with socket exhaustion. Ideally our function apps will be on our regional vnet, along with the CosmosDB account and storage accounts. The legacy proxy could remain on the internet and communicate with function apps via their private endpoints, solving both problems.

There's no vnet support in APIM on the consumption tier. The required premium tier of APIM is wildly, unmanageably expensive just to obtain this vnet feature. This APIM migration guidance assumes that we need the vast functionality of APIM and can swallow the cost. This is simply not possible with our customers, business model, or scale.