Private Google Access vs Public IP: Security Explained

When you deploy virtual machines in Google Cloud Platform, you face a fundamental security decision that many engineers overlook until it becomes a problem. Your VMs need to interact with Google Cloud services like Cloud Storage, BigQuery, or Pub/Sub. The question is whether those VMs need public IP addresses to do so.

The common assumption is straightforward: if a VM needs to talk to an API, it needs a route to the internet. This leads teams to assign public IPs to their compute resources almost by default. But this approach exposes your infrastructure to the public internet unnecessarily, expanding your attack surface and creating security risks that could be entirely avoided.

Private Google Access changes this equation completely. It allows your VMs to reach Google Cloud APIs and services without ever touching the public internet, and without requiring public IP addresses. Understanding when and how to use this capability is essential for building secure, production-ready architectures on GCP.

The Security Difference

Consider a data processing pipeline running on Compute Engine instances. These VMs read files from Cloud Storage, write results to BigQuery, and publish completion messages to Pub/Sub. Without Private Google Access, each VM would need a public IP address to reach these services. That public IP makes the VM addressable from anywhere on the internet.

Even with firewall rules blocking inbound traffic, the existence of that public IP creates risk. Your VM now has a presence on the public internet. It can be scanned, probed, and targeted. Security vulnerabilities in the networking stack or misconfigurations in your firewall rules become pathways for potential attacks.

With Private Google Access enabled on your subnet, the same VMs can operate with only internal IP addresses. They remain completely isolated from the public internet while maintaining full connectivity to Google Cloud services. The traffic flows through Google's private network infrastructure rather than traversing the public internet.

This difference matters for security posture. A VM without a public IP cannot be directly reached from the internet, period. There's no IP address to scan, no endpoint to probe. Your attack surface shrinks dramatically.

How Private Google Access Actually Works

Private Google Access is a subnet-level configuration in your VPC network. When you enable it on a subnet, any VM in that subnet gains the ability to reach Google APIs through internal routing, regardless of whether the VM has an external IP address.

Imagine you have two VPC networks in your Google Cloud environment. In VPC Network A, you create a subnet with Private Google Access enabled and deploy a VM with only an internal IP address (something like 10.128.0.5). This VM needs to upload processed data to a Cloud Storage bucket and insert records into BigQuery.

Because Private Google Access is enabled, the VM can reach the Cloud Storage API and BigQuery API directly. The traffic routes through Google's internal network backbone. The VM sends requests to the public API endpoints (like storage.googleapis.com), but those requests never traverse the public internet. Google's network infrastructure routes them internally.

In VPC Network B, you create a subnet without Private Google Access enabled. You deploy a similar VM with the same internal IP requirements. This VM also needs to access Cloud Storage and BigQuery. However, without Private Google Access, the VM can't reach those services unless it has a public IP address assigned.

When that VM tries to connect to storage.googleapis.com, the connection fails. There's no route from the internal-only VM to the Google APIs. To make this work, you would need to assign a public IP address to the VM. Once it has that public IP, the VM can reach Google APIs, but the traffic flows out through a Cloud NAT gateway or the VM's public IP, across the public internet, and back to Google's API endpoints.

When This Configuration Matters

For a genomics research lab processing DNA sequencing data, Private Google Access becomes critical. Their Compute Engine VMs analyze massive datasets stored in Cloud Storage buckets containing sensitive patient information. These VMs have no legitimate reason to communicate with the public internet. They read data from Cloud Storage, perform analysis, and write results back to BigQuery.

Enabling Private Google Access on the subnet where these VMs run means the entire processing pipeline operates without public IPs. The data never leaves Google's network infrastructure. If a vulnerability were discovered in one of the analysis tools running on these VMs, attackers would have no network path to exploit it remotely. The VMs simply aren't reachable from outside the VPC.

Similarly, consider a mobile game studio running a real-time analytics platform. Their Dataflow pipelines process player event streams and write aggregated statistics to BigQuery. The Dataflow workers are ephemeral VMs that spin up and down based on processing demand. These workers need access to Cloud Storage for temporary files and BigQuery for output, but they have no need for public internet access.

With Private Google Access enabled, the Dataflow service can launch hundreds of worker VMs with only internal IPs. The workers operate securely while maintaining full access to the Google Cloud services they need. The attack surface remains minimal even as the infrastructure scales dynamically.

The Public IP Alternative and Its Costs

Without Private Google Access, you face a difficult choice. You can assign public IPs to your VMs, which works functionally but creates the security exposure we've discussed. Alternatively, you can set up Cloud NAT to allow VMs with only internal IPs to reach the internet.

Cloud NAT provides a managed network address translation service. VMs without public IPs can send traffic to internet destinations (including Google APIs) through the NAT gateway. This keeps individual VMs from having their own public IPs, which is better than assigning public IPs directly.

However, Cloud NAT still routes your API traffic across the public internet. The connection to storage.googleapis.com leaves your VPC, traverses public networks, and arrives at Google's API endpoints. While the connection is encrypted, it's exposed to internet routing and potential interception. You also pay for NAT gateway processing and egress bandwidth.

Private Google Access eliminates both concerns. Traffic stays on Google's private network, and there's no additional charge for using Private Google Access itself. You pay only for the API usage and any associated data transfer, the same costs you would incur regardless of how the traffic was routed.

Configuration Subtleties Worth Understanding

Private Google Access applies specifically to Google APIs and services. It doesn't provide access to arbitrary internet destinations. A VM with only an internal IP in a subnet with Private Google Access enabled can reach BigQuery and Cloud Storage, but it can't download packages from an external package repository or make API calls to a third-party service.

If your VMs need both Google API access and selective public internet access, you would typically enable Private Google Access and also configure Cloud NAT. The Private Google Access routes handle traffic to Google services efficiently and securely, while Cloud NAT provides the gateway for other internet-bound traffic.

The feature also works with VPC Service Controls. A hospital network might use VPC Service Controls to create a security perimeter around sensitive patient data in BigQuery and Cloud Storage. VMs within that perimeter can access the protected resources through Private Google Access without any special configuration. The access controls and audit logging work identically whether the VM has a public IP or not.

One common point of confusion involves domain name resolution. When you enable Private Google Access, Google Cloud automatically configures DNS to resolve Google API domains to special internal IP addresses. Your VM still connects to storage.googleapis.com by name, but that name resolves to an IP address that routes through Google's internal network rather than the public internet. This happens transparently, requiring no changes to your application code.

Making the Right Decision for Your Architecture

The decision to enable Private Google Access should be straightforward for resources that only interact with Google Cloud services. If your VMs are running data processing jobs, machine learning training, batch analytics, or similar workloads that consume and produce data within Google Cloud, Private Google Access should be enabled by default.

For a subscription box service processing customer orders, the VMs that handle order data from Pub/Sub, update inventory in Firestore, and generate shipping labels might legitimately need public internet access to communicate with shipping carrier APIs. Even in this scenario, you would enable Private Google Access on the subnet. The VMs would get their Google Cloud API access through the private route, and you would separately configure Cloud NAT for the external API calls. This gives you the security benefits of Private Google Access while maintaining the necessary external connectivity.

The configuration is subnet-specific, which allows you to design networks with different security zones. A solar farm monitoring system might have one subnet for edge processing VMs that collect sensor data and only need to write to Cloud Storage, with Private Google Access enabled and no internet access. A separate subnet might host management VMs that need both Google Cloud access and internet connectivity for software updates, with both Private Google Access and Cloud NAT configured.

What This Means for Production Systems

Private Google Access represents a fundamental principle of cloud security: minimize exposure by limiting connectivity to what's actually necessary. Your VMs need to reach Google Cloud APIs. They don't need to be reachable from the internet, and in many cases they don't need to reach the internet either.

Enabling this feature requires a single checkbox when you create or modify a subnet. The impact on your security posture is substantial. Every VM in that subnet that would otherwise need a public IP can now operate with only an internal address, invisible to the public internet.

This becomes particularly important as you scale. A freight logistics company might run hundreds of Compute Engine instances processing shipment tracking data. Each instance without Private Google Access would need either a public IP or NAT capacity. With Private Google Access, those hundreds of instances operate securely with internal IPs, accessing Cloud Storage and BigQuery through Google's private network.

The feature also simplifies compliance requirements. When you can demonstrate that processing VMs have no public internet exposure, security audits become more straightforward. For a payment processor handling sensitive financial transactions, showing that data processing infrastructure is network-isolated except for necessary Google Cloud service access addresses many compliance questions before they're asked.

Key Takeaways

Private Google Access should be your default configuration for subnets hosting VMs that interact with Google Cloud services. The security benefit of removing public IP addresses from your compute resources far outweighs the minimal effort required to enable the feature.

Remember that Private Google Access is subnet-specific. You enable it when creating a subnet or modify existing subnets to enable it. Once enabled, all VMs in that subnet benefit immediately, including VMs that already exist.

The feature doesn't restrict your VMs from having public IPs if they need them for other reasons. It simply makes public IPs unnecessary for reaching Google Cloud APIs. You can enable Private Google Access and still assign public IPs to VMs that genuinely need internet connectivity.

When designing VPC networks for production workloads, consider the connectivity requirements carefully. VMs that only process data within Google Cloud should operate in subnets with Private Google Access enabled and no public IPs assigned. This reduces your attack surface and simplifies your security model without sacrificing any functionality.

Building Secure GCP Architectures

Understanding Private Google Access is part of building secure, well-architected systems on Google Cloud Platform. The principle extends beyond this single feature: grant only the connectivity that your workloads actually require. Private Google Access makes that principle practical for the common scenario of VMs that need to interact with GCP services.

As you work more with Google Cloud networking, you'll encounter this pattern repeatedly. The platform provides mechanisms to keep traffic private, to route it efficiently, and to maintain security without sacrificing functionality. Private Google Access is one of the clearest examples of this design philosophy.

Getting comfortable with these networking concepts takes practice and hands-on experience. For readers preparing for the Google Cloud Professional Data Engineer certification or looking to deepen their understanding of GCP security patterns, comprehensive resources can speed up your learning. Those looking for structured exam preparation can check out the Professional Data Engineer course, which covers networking, security, and data architecture patterns in depth.

The security difference between Private Google Access and public IP access is significant. One approach keeps your infrastructure isolated and secure while maintaining full Google Cloud functionality. The other exposes your resources unnecessarily. The choice should be clear for resources that don't need public internet exposure.