The correct answer is an ingress firewall rule allowing TCP port 443 from source 0.0.0.0/0, applied to instances with the target tag 'https-server'. This configuration is necessary because a Compute Engine instance with a public IP must have an ingress rule to accept incoming traffic from the internet; specifying TCP:443 restricts the rule to HTTPS only, while source 0.0.0.0/0 covers all external IPs. The target tag ensures the rule applies selectively to the intended instance rather than all VMs in the subnet. On the Google Professional Cloud Architect exam, this scenario tests your understanding of VPC firewall rules, particularly the distinction between ingress and egress, and the use of target tags for granular control. A common trap is confusing ingress with egress or forgetting that a public IP alone does not open ports—firewall rules are mandatory. Memory tip: "HTTPS from the web? Ingress on port 443, tag your server, source all IPs."
Google PCA Manage and provision cloud infrastructure Practice Question
This PCA practice question tests your understanding of manage and provision cloud infrastructure. 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.
An organization has a VPC with two subnets: subnet-a (10.0.1.0/24) and subnet-b (10.0.2.0/24). They launched a Compute Engine instance in subnet-a with an internal IP 10.0.1.2 and a public IP. They want the instance to only allow HTTPS traffic from the internet. Which firewall rule should they create?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ingress rule: allow tcp:443, source 0.0.0.0/0, target tag 'https-server'
Option D is correct because the instance needs to accept incoming HTTPS traffic (TCP port 443) from the internet. An ingress firewall rule with source 0.0.0.0/0 allows traffic from any external IP, and applying it to instances with the target tag 'https-server' ensures only tagged instances are affected. This matches the requirement to allow only HTTPS from the internet.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Ingress rule: allow tcp:0-65535, source 0.0.0.0/0, target tag 'https-server'
Egress rule: allow tcp:443, destination 0.0.0.0/0, target tag 'https-server'
Why it's wrong here
Egress rules control outbound traffic; inbound HTTPS from internet requires ingress rule.
✗
Ingress rule: allow tcp:443, source 10.0.0.0/16, target tag 'https-server'
Why it's wrong here
This allows HTTPS only from internal IPs, not the internet.
✓
Ingress rule: allow tcp:443, source 0.0.0.0/0, target tag 'https-server'
Why this is correct
This rule correctly allows inbound HTTPS from any source to instances with the tag.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse ingress vs. egress rules or mistakenly restrict the source to the VPC range (10.0.0.0/16) thinking it includes the internet, when in fact it only allows traffic from within the VPC.
Detailed technical explanation
How to think about this question
In Google Cloud VPC, firewall rules are stateful: if an ingress rule allows traffic, the corresponding return egress traffic is automatically permitted. The target tag mechanism allows selective application of rules to instances, which is more scalable than using source ranges or service accounts when managing multiple instances. The source 0.0.0.0/0 in an ingress rule matches any IPv4 address, including public internet clients, but does not affect traffic within the VPC unless explicitly allowed.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Manage and provision cloud infrastructure — This question tests Manage and provision cloud infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ingress rule: allow tcp:443, source 0.0.0.0/0, target tag 'https-server' — Option D is correct because the instance needs to accept incoming HTTPS traffic (TCP port 443) from the internet. An ingress firewall rule with source 0.0.0.0/0 allows traffic from any external IP, and applying it to instances with the target tag 'https-server' ensures only tagged instances are affected. This matches the requirement to allow only HTTPS from the internet.
What should I do if I get this PCA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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