What is Private Google Access?

Key Concepts:

• Private Google Access (PGA)
• VPC Subnet
• Compute Engine Instance
• External IP Address
• Google APIs and Services
• Cloud Front Ends (CFEs)
• Cloud Path
• Internet Gateway
• Default Route (0.0.0.0/0)

1. Introduction to Private Google Access (PGA)

• Normally, Compute Engine instances require a public IP address to access internet resources, including Google APIs and services.
• Using external IP addresses increases an organization's security risk by exposing the network to the internet.
• PGA allows Compute Engine instances on a VPC subnet to securely access Google APIs and services without needing an external IP address or Cloud NAT.

2. How Private Google Access Works

• VPC Network Example: A VPC network with two subnets (A and B), each containing two virtual machines. Only two VMs have public IP addresses.
• Default Route and Internet Gateway: VMs typically need a default route (0.0.0.0/0) pointing to the internet gateway to reach destinations outside the VPC. The internet gateway acts as the exit point for packets leaving the VPC.
• Enabling PGA on a Subnet: PGA can be enabled on individual VPC subnets without downtime.
• Cloud Front Ends (CFEs): CFEs are reverse proxies for most Google APIs (e.g., Cloud Storage, BigQuery, Cloud Pub/Sub, Compute Engine).
• Cloud Path: After enabling PGA on a subnet, VMs can send network traffic with their internal source IP addresses to CFEs using Cloud Path. Cloud Path is an optimized routing path within Google's network that connects GCP resources directly to Google APIs and services.
• VMs with external IP addresses also use Cloud Path to communicate with Google APIs. PGA extends this capability to VMs without external IPs.

3. Benefits of Private Google Access

• Enhanced Security: Reduces VM exposure by eliminating the need for external IPs when communication is limited to Google APIs.
• Simplified Network Configuration: Simplifies network setup in scenarios where only Google APIs need to be accessed.
• Reduced Operational Cost: Lowers operational expenses by avoiding the need for external IPs and related infrastructure.

4. Limitations of Private Google Access

• PGA and Cloud Path do not apply when connecting to other public IP addresses on the internet, including Google Cloud Load Balancers and Compute Instances.
• A complete, up-to-date list of supported Google APIs and services for Private Google Access can be found in the official Google Cloud documentation.

5. Conclusion

Private Google Access provides a secure and efficient way for Compute Engine instances to access Google APIs and services without exposing them to the public internet. By utilizing Cloud Path and CFEs, PGA enhances security, simplifies network configuration, and reduces operational costs. However, it's important to note its limitations regarding access to other public IP addresses and to consult the official Google Cloud documentation for the latest supported services.