The answer is to use VPC Service Controls and Private Google Access. This combination is correct because Private Google Access allows on-premises resources connected via Cloud VPN to reach Google APIs and services, including Pub/Sub, using internal IP addresses rather than traversing the public internet, while VPC Service Controls provides a security perimeter that prevents data exfiltration from the authorized VPC. On the Google Professional Cloud Developer exam, this scenario tests your understanding of hybrid cloud pub/sub access via VPN, often appearing as a distractor where candidates mistakenly choose options related to dynamic routing or internet gateways. A common trap is assuming that Cloud VPN alone enables API access, but you must explicitly enable Private Google Access on the subnet and apply VPC Service Controls for secure, private connectivity. Remember the mnemonic “VPN + PGA + VPC SC” to recall that a VPN connection requires both Private Google Access and VPC Service Controls for secure hybrid pub/sub publishing.
PCD Integrating Google Cloud services Practice Question
This PCD practice question tests your understanding of integrating google cloud services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has a hybrid cloud setup with on-premises applications that need to send messages to a Pub/Sub topic. The on-premises network is connected via Cloud VPN. What is the recommended way to publish messages?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use VPC Service Controls and Private Google Access
Option A is correct because to allow on-premises access to Pub/Sub via VPN, you need to enable Private Google Access and use VPC Service Controls for security. Option B is for dynamic routing, not for accessing Pub/Sub. Option C is for dynamic routing, not for Pub/Sub access. Option D is for outbound internet access, not for private access to Google APIs.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use a Cloud NAT instance to route traffic
Why it's wrong here
Cloud NAT is for outbound internet access, not for private access to Google APIs.
✗
Expose Pub/Sub publicly and use authentication via OAuth2 tokens
Why it's wrong here
Exposing Pub/Sub publicly is not recommended for security reasons.
✓
Use VPC Service Controls and Private Google Access
Why this is correct
Private Google Access enables on-premises to reach Google APIs via VPN, and VPC Service Controls provides security.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use Cloud Router to establish BGP sessions for direct connectivity
Why it's wrong here
Cloud Router is for dynamic routing, not for accessing Pub/Sub.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCD NAT questions on configuration and troubleshooting.
Integrating Google Cloud services — This question tests Integrating Google Cloud services — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use VPC Service Controls and Private Google Access — Option A is correct because to allow on-premises access to Pub/Sub via VPN, you need to enable Private Google Access and use VPC Service Controls for security. Option B is for dynamic routing, not for accessing Pub/Sub. Option C is for dynamic routing, not for Pub/Sub access. Option D is for outbound internet access, not for private access to Google APIs.
What should I do if I get this PCD question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCD NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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