This PCDOE practice question tests your understanding of optimizing service performance. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 runs a microservices architecture on GKE with Istio service mesh. They observe that service-to-service latency has increased after enabling mTLS. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
mTLS encryption overhead
Encrypting and decrypting each request adds CPU overhead and latency.
Incorrect load balancer configuration
Why wrong: mTLS is a service mesh feature, unrelated to load balancer.
Network policy restriction
Why wrong: Network policies may drop traffic but typically don't add noticeable latency.
Sidecar proxy resource limits
Why wrong: Resource limits can cause throttling, but the question points to mTLS as the change.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
mTLS encryption overhead
Enabling mTLS in Istio encrypts all service-to-service traffic using mutual TLS, which adds CPU overhead for encryption and decryption of each request. This encryption overhead directly increases latency, especially for high-throughput or small-payload services, as the sidecar proxies must perform TLS handshakes and cryptographic operations on every packet.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
mTLS encryption overhead
Why this is correct
Encrypting and decrypting each request adds CPU overhead and latency.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Incorrect load balancer configuration
Why it's wrong here
mTLS is a service mesh feature, unrelated to load balancer.
Network policy restriction
Why it's wrong here
Network policies may drop traffic but typically don't add noticeable latency.
Sidecar proxy resource limits
Why it's wrong here
Resource limits can cause throttling, but the question points to mTLS as the change.
Common exam traps
Google Cloud often tests the misconception that mTLS only adds security without performance impact, but candidates must recognize that encryption/decryption at the sidecar proxy level introduces measurable CPU-bound latency.
Detailed technical explanation
mTLS in Istio uses Envoy proxies as sidecars that terminate TLS from the client side and re-encrypt to the server side, requiring two full TLS handshakes per connection. The overhead is most noticeable with frequent short-lived connections, as each new connection incurs the cost of certificate verification and cipher negotiation, while long-lived connections amortize the handshake cost over many requests.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Optimizing service performance — This question tests Optimizing service performance — Read the scenario before looking for a memorised answer..
The correct answer is: mTLS encryption overhead — Enabling mTLS in Istio encrypts all service-to-service traffic using mutual TLS, which adds CPU overhead for encryption and decryption of each request. This encryption overhead directly increases latency, especially for high-throughput or small-payload services, as the sidecar proxies must perform TLS handshakes and cryptographic operations on every packet.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCDOE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDOE exam.
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