A new microservice (Service A) deployed on Cloud Run needs to securely and privately call another internal microservice (Service B) also deployed on…

To ensure Service A calls Service B privately without traversing the public internet, and that Service B is only accessible from the VPC, a specific network configuration is required.

1. Service A Egress: For Service A (Cloud Run) to send traffic to a resource within a VPC, it must use a Serverless VPC Access connector. This routes egress traffic from the serverless environment into the specified VPC.

2. Service B Ingress: To make Service B accessible only from within the VPC, its ingress setting must be configured to 'Internal and Cloud Load Balancing'. This setting ensures that the service can only be reached through an Internal HTTP(S) Load Balancer, whose frontend is an IP address within the VPC.

This combination creates a fully private communication path from Service A, through the VPC, to Service B.

A: Cloud Run services are serverless and do not reside within a specific VPC that can be peered. This option misunderstands the fundamental networking model of Cloud Run.

B: The 'Internal' ingress setting is less restrictive, allowing traffic from other serverless services in the project, not just from the VPC. The run.invoker role handles authentication, not the network path.

D: Setting ingress to 'Allow all traffic' exposes Service B to the public internet, directly violating the core requirement for private, internal-only communication.

1. Google Cloud Documentation, Cloud Run Networking, "Controlling ingress settings": This document details the three ingress settings. It specifies that "Internal and Cloud Load Balancing" restricts ingress to traffic from internal HTTP(S) load balancers, which is the mechanism for VPC-only access.

Reference: Google Cloud Documentation > Cloud Run > Networking > "Controlling ingress settings".

2. Google Cloud Documentation, Serverless VPC Access, "Overview": This page explains that Serverless VPC Access connectors allow serverless services like Cloud Run to send requests to a VPC network. This is required for Service A to initiate a private connection.

Reference: Google Cloud Documentation > Serverless VPC Access > "Overview".

3. Google Cloud Documentation, "Set up an internal HTTP(S) load balancer with Cloud Run": This tutorial outlines the end-to-end process. It states, "By using an internal HTTP(S) load balancer, you can ensure that requests to your serverless apps are sent from clients within your VPC network... To enforce that all requests come from the internal HTTP(S) load balancer, set the ingress setting of the Cloud Run service to internal-and-cloud-load-balancing."

Reference: Google Cloud Documentation > Load Balancing > "Set up an internal HTTP(S) load balancer with Cloud Run".