Enabling Private Google Access allows Compute Engine VMs that have only internal IP addresses to reach Google APIs privately without needing external IPs. Using private DNS to direct Google API names to the restricted Google APIs VIPs ensures the VMs reach the Cloud Storage API over Google-controlled endpoints while reducing exposure to the public internet path for API access.

By configuring a VPC Service Controls perimeter around project XYZ, you can create a secure boundary around the project and restrict access to Cloud Storage to only those instances that are within the VPCs under project XYZ. You can include storage.googleapis.com as a restricted service in the service perimeter, which will ensure that only authorized VPCs can access the Cloud Storage bucket containing sensitive data.
https://cloud.google.com/vpc/docs/private-access-options
https://cloud.google.com/vpc/docs/configure-private-service-connect-apis

Option B is the Correct choice because, Cloud Composer is a managed Apache Airflow service that helps you create, schedule, monitor and manage workflows.
Option A is Incorrect choice because, you could install Apache Airflow on a VM instance but it would mean you will have to manage the infrastructure.
Option C is Incorrect because, Istio an open platform to connect, monitor, and secure microservices.
Option D is Incorrect because, Stackdriver is a monitoring and management for services, containers, applications, and infrastructure.

Cloud NAT with Custom Source Ranges: Cloud NAT allows you to configure a custom source range that limits which subnets can use it for outbound internet access. By specifying the allowed subnets only, you can ensure that no unauthorized subnet can unintentionally or maliciously use Cloud NAT for egress.
Cloud NAT Rules for Subnet-Specific Control: Configuring rules in Cloud NAT allows fine-grained control over which subnets have access to the internet. This aligns with Google-recommended practices for securing internet access and avoiding configuration errors.
Avoiding Unintentional Configuration Issues: By using Cloud NAT's built-in configuration options (custom source ranges and NAT rules), you eliminate the need for additional firewall rules or complex organizational policies, reducing the likelihood of misconfiguration by administrators.

Policy-based VPNs require explicit configuration of traffic selectors, known as LOCAL_TS (local traffic selector) and REMOTE_TS (remote traffic selector), which define the specific subnet ranges allowed to pass through the VPN tunnel.
1. Set LOCAL_TS to your on-premises subnets: Since on-premises subnets are 172.16.100.0/24,
172.16.101.0/24, and 172.16.102.0/24, they should be included in the LOCAL_TS.
2. Set REMOTE_TS to your Google Cloud subnets: Google Cloud subnets are 192.168.100.0/24,
192.168.101.0/24, and 192.168.102.0/24, so they should be included in the REMOTE_TS.
3. Match specific subnets: Policy-based VPNs require a one-to-one mapping of the traffic selectors.
Wildcard ranges (e.g., /22 or 0.0.0.0/0) cannot be used because policy-based VPNs rely on matching specific subnet ranges to establish secure connectivity.