The answer is that existing connections to the failed instance are terminated immediately. This occurs because the internal TCP/UDP load balancer, when paired with an unmanaged instance group, does not support connection draining; it operates strictly at Layer 4 and has no mechanism to gracefully close TCP flows or wait for application-level cleanup once a health check fails. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding of the critical difference between managed and unmanaged instance groups regarding load balancer behavior—a common trap is assuming that connection draining applies universally, but it is only available with managed instance groups. Remember the memory tip: "Unmanaged means ungraceful"—if the group is unmanaged, expect abrupt termination, not a graceful drain.
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 an internal TCP/UDP load balancer to distribute traffic to a backend service. The backend instances are in an unmanaged instance group. Some instances fail health checks and are removed. What happens to existing connections to failed instances?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Existing connections are terminated immediately.
When an instance in an unmanaged instance group fails a health check, the internal TCP/UDPload balancer immediately terminates all existing connections to that instance. This is because the load balancer does not support connection draining for unmanaged instance groups; it simply stops forwarding new traffic and drops existing flows to the failed instance. The abrupt termination occurs because the load balancer operates at Layer 4 and has no mechanism to gracefully close TCP connections or wait for application-level cleanup.
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.
✗
The load balancer drains existing connections before removing the instance.
Why it's wrong here
Internal TCP/UDP load balancers do not support connection draining.
✗
Existing connections are seamlessly redirected to healthy instances.
Why it's wrong here
The load balancer does not maintain session state for existing connections after instance removal.
✓
Existing connections are terminated immediately.
Why this is correct
Internal TCP/UDP load balancers do not provide connection draining; connections are dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
The load balancer waits for all existing connections to close before removing the instance.
Why it's wrong here
The load balancer removes the instance immediately without waiting.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume connection draining is always available for load balancers, but Cisco tests the distinction between managed and unmanaged instance groups, where unmanaged groups lack graceful connection termination features.
Detailed technical explanation
How to think about this question
Under the hood, the internal TCP/UDPload balancer uses a hash-based forwarding mechanism (e.g., 5-tuple hash for TCP) to pin a connection to a specific backend instance. When that instance is removed, the hash entry is invalidated, and any subsequent packets for that flow are dropped, causing a TCP reset (RST) or simply no response. In a real-world scenario, this can cause partial data loss or transaction failures for clients that were mid-request, which is why managed instance groups with connection draining (up to 3600 seconds) are preferred for stateful applications.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Existing connections are terminated immediately. — When an instance in an unmanaged instance group fails a health check, the internal TCP/UDP load balancer immediately terminates all existing connections to that instance. This is because the load balancer does not support connection draining for unmanaged instance groups; it simply stops forwarding new traffic and drops existing flows to the failed instance. The abrupt termination occurs because the load balancer operates at Layer 4 and has no mechanism to gracefully close TCP connections or wait for application-level cleanup.
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.
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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