Private Google Access in GCP - Deep Dive

Overview - Private Google Access

What is it?

Private Google Access is a feature in Google Cloud that allows virtual machines (VMs) without external IP addresses to reach Google services securely. It lets these VMs connect to Google APIs and services using internal IP addresses only, without exposing them to the public internet. This keeps the communication private and secure within Google's network.

Why it matters

Without Private Google Access, VMs without public IPs cannot reach Google services, limiting their functionality or forcing insecure workarounds. This feature solves the problem by enabling secure, private access to essential Google APIs, improving security and compliance. It helps organizations keep their cloud resources isolated while still using Google’s powerful services.

Where it fits

Before learning Private Google Access, you should understand basic Google Cloud networking concepts like VPCs, subnets, and IP addressing. After this, you can explore advanced networking features like Private Service Connect and VPC Service Controls to further secure and manage service access.

Mental Model

Core Idea

Private Google Access lets internal-only machines reach Google services privately without needing public internet addresses.

Think of it like...

It's like having a private hallway inside a building that connects your office directly to the mailroom, so you can send and receive mail without stepping outside or using the public lobby.

┌───────────────┐       ┌─────────────────────┐
│ VM without    │       │ Google APIs &       │
│ public IP    │──────▶│ Services (Private)   │
│ (Internal IP) │       │                     │
└───────────────┘       └─────────────────────┘
        ▲
        │
   Private Google Access enabled subnet
        │
        ▼
┌─────────────────────┐
│ VPC Network         │
│ (No public internet)│
└─────────────────────┘

Build-Up - 7 Steps

1

Foundation

Understanding VMs Without Public IPs

Concept: Learn what it means for a VM to have no public IP and how it affects connectivity.

In Google Cloud, a VM can have an internal IP address only, meaning it is not reachable from the internet directly. This setup improves security by isolating the VM from public access. However, without a public IP, the VM cannot reach external services on the internet by default, including Google APIs.

Result

You understand that VMs without public IPs are isolated from the internet and cannot access Google services by default.

Knowing that internal-only VMs lack internet access explains why special features like Private Google Access are needed to connect them to Google services.

2

Foundation

What Are Google APIs and Services?

Concept: Identify the Google services that VMs often need to access, such as Cloud Storage and BigQuery.

Google Cloud offers many APIs and services that VMs use to store data, analyze information, or manage resources. Examples include Cloud Storage for files, BigQuery for data analysis, and Cloud Pub/Sub for messaging. Accessing these services usually requires network connectivity to Google's endpoints.

Result

You recognize the importance of Google APIs for cloud workloads and the need for VMs to reach them.

Understanding the role of Google APIs clarifies why VMs need a way to connect securely, even without public IPs.

3

Intermediate

How Private Google Access Works

🤔Before reading on: do you think Private Google Access routes traffic through the public internet or stays within Google's network? Commit to your answer.

Concept: Private Google Access routes traffic from internal-only VMs to Google services using Google's private network, not the public internet.

When Private Google Access is enabled on a subnet, VMs in that subnet can send requests to Google APIs using their internal IPs. Google Cloud routes this traffic internally through its private network, ensuring it never leaves Google's infrastructure or goes through the public internet. This keeps data secure and reduces exposure to external threats.

Result

VMs without public IPs can access Google services privately and securely.

Knowing that traffic stays inside Google's network explains how Private Google Access enhances security and reliability.

4

Intermediate

Enabling Private Google Access on Subnets

🤔Before reading on: do you think Private Google Access is enabled per VM or per subnet? Commit to your answer.

Concept: Private Google Access is enabled at the subnet level, affecting all VMs within that subnet.

To use Private Google Access, you enable it on a subnet in your VPC network. All VMs in that subnet without public IPs automatically gain private access to Google services. This centralized control simplifies management and ensures consistent behavior for all VMs in the subnet.

Result

You can configure your network so internal-only VMs access Google services without public IPs.

Understanding subnet-level control helps manage access efficiently and avoid misconfigurations.

5

Intermediate

Limitations of Private Google Access

🤔Before reading on: do you think Private Google Access allows access to all internet services or only Google APIs? Commit to your answer.

Concept: Private Google Access only allows access to Google APIs and services, not the entire internet.

Private Google Access does not provide general internet access. VMs still cannot reach external websites or services outside Google Cloud unless they have public IPs or use other methods like Cloud NAT. This feature is specifically for private access to Google-managed services.

Result

You know the scope of Private Google Access and its boundaries.

Recognizing this limitation prevents incorrect assumptions about internet connectivity for internal-only VMs.

6

Advanced

Combining Private Google Access with Cloud NAT

🤔Before reading on: do you think Cloud NAT is needed if Private Google Access is enabled? Commit to your answer.

Concept: Cloud NAT provides internet access for internal-only VMs, complementing Private Google Access which only covers Google services.

If your VMs need to access the internet beyond Google APIs, you can use Cloud NAT. Cloud NAT lets VMs without public IPs send outbound traffic to the internet securely. Private Google Access and Cloud NAT together provide full connectivity: private access to Google services and controlled internet access.

Result

You can design networks that balance security and connectivity for internal-only VMs.

Knowing how these features complement each other helps build secure, functional cloud networks.

7

Expert

Internal Routing and DNS for Private Google Access

🤔Before reading on: do you think DNS resolution changes when Private Google Access is enabled? Commit to your answer.

Concept: Private Google Access relies on special DNS and routing to direct Google API requests internally without public IPs.

When Private Google Access is enabled, Google Cloud provides special DNS entries that resolve Google API hostnames to internal IP addresses. The VPC routes these requests through Google's private network. This internal DNS and routing setup is transparent to the VM but critical for private connectivity. Misconfigurations in DNS or routing can break access.

Result

You understand the invisible plumbing that makes Private Google Access work.

Understanding DNS and routing under the hood helps troubleshoot and optimize private access setups.

Under the Hood

Private Google Access works by intercepting requests from VMs without public IPs destined for Google APIs. The DNS resolves API hostnames to internal Google IPs. The VPC network routes these requests through Google's private backbone network instead of the public internet. This routing uses internal IP ranges and special gateways managed by Google, ensuring traffic stays within Google's infrastructure securely.

Why designed this way?

Google designed Private Google Access to improve security and compliance by avoiding public internet exposure for sensitive workloads. Alternatives like giving VMs public IPs or using proxies were less secure or more complex. This design balances ease of use, security, and performance by leveraging Google's global private network and DNS.

┌───────────────┐          ┌─────────────────────┐
│ VM (No Public │          │ Google DNS resolves  │
│ IP, Internal) │─────────▶│ googleapis.com to    │
└───────────────┘          │ internal IP address  │
                           └─────────┬───────────┘
                                     │
                           ┌─────────▼───────────┐
                           │ Google Private      │
                           │ Network Routing     │
                           └─────────┬───────────┘
                                     │
                           ┌─────────▼───────────┐
                           │ Google APIs &       │
                           │ Services            │
                           └─────────────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Does Private Google Access give your VM full internet access? Commit to yes or no.

Common Belief: Private Google Access allows VMs without public IPs to access the entire internet.

Reality: It only allows access to Google APIs and services, not the general internet.

Why it matters: Assuming full internet access can lead to failed connections and security gaps if other internet access methods are not configured.

Quick: Is Private Google Access enabled per VM or per subnet? Commit to your answer.

Common Belief: You enable Private Google Access on individual VMs.

Reality: It is enabled on the subnet level, affecting all VMs within that subnet.

Why it matters: Misunderstanding this can cause inconsistent access and configuration errors.

Quick: Does Private Google Access route traffic through the public internet? Commit to yes or no.

Common Belief: Traffic to Google APIs from internal VMs goes through the public internet.

Reality: Traffic stays within Google's private network, never touching the public internet.

Why it matters: This affects security posture and compliance; assuming public routing may cause unnecessary firewall rules or audits.

Quick: Can Private Google Access be used to access third-party services? Commit to yes or no.

Common Belief: Private Google Access allows private access to any internet service.

Reality: It only works for Google-managed APIs and services.

Why it matters: Expecting broader access can cause confusion and failed connections.

Expert Zone

1

Private Google Access relies heavily on Google’s internal DNS; custom DNS setups can break it if not configured properly.

2

Enabling Private Google Access does not automatically grant access permissions; IAM roles and service accounts still control API access.

3

Traffic through Private Google Access is subject to Google’s network policies and may have different latency or routing than public internet paths.

When NOT to use

Do not rely on Private Google Access if your VMs need to access non-Google internet services; use Cloud NAT or VPNs instead. Also, if you require fine-grained control over service endpoints, consider Private Service Connect or VPC Service Controls.

Production Patterns

In production, Private Google Access is commonly combined with Cloud NAT to provide both private Google API access and controlled internet access. It is also used alongside VPC Service Controls to enforce security boundaries. Enterprises often enable it on dedicated subnets for sensitive workloads to minimize attack surface.

Connections

Cloud NAT

complements

Understanding Private Google Access alongside Cloud NAT helps design networks that balance private service access with controlled internet connectivity.

VPC Service Controls

builds-on

Private Google Access works well with VPC Service Controls to create secure perimeters around Google Cloud resources, enhancing data protection.

Corporate VPNs

similar pattern

Like Private Google Access keeps traffic inside Google’s network, corporate VPNs keep traffic inside a company’s private network, showing a shared principle of private routing for security.

Common Pitfalls

#1 Expecting Private Google Access to provide full internet access for internal-only VMs.

Wrong approach:

VMs without public IPs try to reach external websites relying only on Private Google Access.

Correct approach:

Use Cloud NAT alongside Private Google Access to enable internet access for internal-only VMs.

Root cause:

Misunderstanding the scope of Private Google Access leads to connectivity failures.

#2 Enabling Private Google Access on individual VMs instead of the subnet.

Wrong approach:

Trying to configure Private Google Access per VM in the Google Cloud Console or CLI.

Correct approach:

Enable Private Google Access on the subnet level in the VPC network settings.

Root cause:

Confusing VM-level and subnet-level network configurations.

#3 Using custom DNS servers without forwarding Google API domains correctly.

Wrong approach:

Setting VMs to use external DNS servers that do not resolve Google API hostnames to internal IPs.

Correct approach:

Ensure DNS settings forward or resolve Google API domains to internal IPs as required by Private Google Access.

Root cause:

Not accounting for DNS resolution requirements breaks private routing.

Key Takeaways

Private Google Access enables VMs without public IPs to securely reach Google APIs using internal IPs only.

It is enabled at the subnet level and does not provide general internet access.

Traffic stays within Google's private network, improving security and compliance.

Combining Private Google Access with Cloud NAT allows both private Google service access and controlled internet connectivity.

Proper DNS and routing configurations are essential for Private Google Access to function correctly.