how can a service run on an Appengine access a DB running on on-premise? cloud vpn, cloud router or both? as far i understand cloud router cna work as a complement with cloud vpn, but i am not sure if cloud router can be used as standalone to solve this type of problem. does appengine standard supports this kind of configuration or we have to use flexible ?
Hello! As you alluded to in your question, App Engine Flexible does support VPC access, so you should be able to connect through that to your own interconnected data centre (via Cloud VPN or what have you, and BGP/routing handled by the Cloud Router).
App Engine Standard has not historically supported VPC access like this, but Google is currently beta-testing a feature that does let you do this (i.e. connect to VPCs) with App Engine Standard, too!