Configure Psc Service Attachment Nat Subnet Firewall

What Private Service Connect NAT Subnets and Firewall Rules Are

Private Service Connect (PSC) allows service producers to expose services privately to consumers across VPC boundaries. When exposing a service via a Service Attachment, the producer VPC requires a dedicated subnetwork specifically allocated with the purpose PRIVATE_SERVICE_CONNECT. This subnetwork acts as a Source Network Address Translation (SNAT) IP pool, translating incoming consumer IP addresses into IP addresses from this designated subnet before packets reach the target instance or internal load balancer.

How It Meets the Requirements

• Subnetwork Configuration: Designating a subnet with purpose = "PRIVATE_SERVICE_CONNECT" reserves a pool of internal IP addresses that Google Cloud uses strictly to perform source address translation on incoming consumer requests.
• Firewall Rule Enforcement: Because the producer endpoint sees all incoming packets as originating from the PSC NAT subnet's IP range rather than the consumer's original VPC CIDR, an ingress firewall rule must explicitly allow incoming TCP traffic from the PSC NAT subnet CIDR range into the destination backend or proxy instance.
• Network Boundary Security: This configuration maintains strict isolation without requiring VPC peering or exposing public IPs, preventing transitive network traversal while securing data in transit.

Key Advantages and Capabilities

• No IP Address Conflicts: Avoids RFC 1918 CIDR overlap between producer and consumer VPCs through automated address translation.
• Granular Access Control: Firewall rules only need to trust the known PSC NAT subnet range rather than dynamic external consumer subnets.
• Unidirectional Connection Flow: Restricts incoming connections strictly to the exposed target service without exposing the rest of the producer's VPC resources.
• High Throughput and Low Latency: Routes packets directly across Google's internal software-defined network infrastructure.

Why This Is Optimal

This is the standard, architecturally required mechanism in Google Cloud networking for configuring published Private Service Connect services. It eliminates IP routing entanglements while enforcing least-privilege ingress filtering via native VPC firewall rules.