The correct configuration is to create a backend service with two backends—one designated as primary and one as failover—and apply a failover policy that triggers when the primary backend becomes unhealthy. This works because Cloud CDN, when paired with an external HTTP(S) load balancer, relies on the backend service’s failover policy to automatically shift traffic away from a backend that fails its health check, routing it to the designated failover backend without manual intervention. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how backend services manage multiple backends and health check integration; a common trap is assuming you need separate load balancers or DNS-based failover, which adds unnecessary complexity. The key distinction is that Cloud CDN’s failover is backend-level, not load-balancer-level. Memory tip: think “backends, not balancers”—the failover policy lives inside the backend service, not on the load balancer itself.
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 uses Cloud CDN with an external HTTP(S) load balancer. They have two origin server groups: a primary in us-central1 and a backup in europe-west1. They want traffic directed to the primary unless it is unhealthy, in which case traffic should fail over to the backup. Which configuration is required?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a backend service with two backends (primary and failover) and a failover policy that marks the primary as failover when unhealthy.
Option D is correct because Cloud CDN with an external HTTP(S) load balancer uses a backend service that can contain multiple backends (e.g., instance groups or NEGs) with a failover policy. When the primary backend is marked as unhealthy by the health check, the load balancer automatically routes traffic to the failover backend. This configuration meets the requirement without manual intervention.
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.
✗
Create a Cloud CDN with two origins and enable failover in the CDN settings.
Why it's wrong here
Cloud CDN itself does not have failover; it relies on the load balancer.
✗
Use a TCP/UDP network load balancer with two target pools.
Why it's wrong here
Network load balancer does not support HTTP health checking or failover policies.
✗
Configure a weighted round-robin with primary weight 100 and backup weight 0, and change weights manually.
Why it's wrong here
This is not automated failover and not recommended.
✓
Create a backend service with two backends (primary and failover) and a failover policy that marks the primary as failover when unhealthy.
Why this is correct
This is the correct architecture for failover across origins.
Clue confirmation
The clue word "primary" in the question point toward this answer.
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 confuse Cloud CDN's origin settings with backend service failover policies, assuming CDN itself handles failover, when in fact failover is a property of the backend service used by the external HTTP(S) load balancer.
Detailed technical explanation
How to think about this question
Under the hood, the backend service's failover policy uses a 'failoverRatio' (default 0.0) and health check status to determine when to send traffic to the failover backend. The primary backend must be in a different region than the failover backend for proper failover behavior. In a real-world scenario, if the primary backend's health check fails for the configured 'unhealthyThreshold' (e.g., 2 consecutive failures), the load balancer automatically shifts traffic to the failover backend, ensuring high availability without manual intervention.
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
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuring network services — This question tests Configuring network services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a backend service with two backends (primary and failover) and a failover policy that marks the primary as failover when unhealthy. — Option D is correct because Cloud CDN with an external HTTP(S) load balancer uses a backend service that can contain multiple backends (e.g., instance groups or NEGs) with a failover policy. When the primary backend is marked as unhealthy by the health check, the load balancer automatically routes traffic to the failover backend. This configuration meets the requirement without manual intervention.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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