Google ACE Planning and configuring a cloud solution Practice Question
This ACE practice question tests your understanding of planning and configuring a cloud solution. 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 has an e-commerce application deployed on Compute Engine instances in a managed instance group (MIG) behind an external HTTP load balancer. The application stores session data in an in-memory cache on each instance. Recently, the team noticed that users are being logged out unexpectedly and losing their shopping cart contents. The MIG is configured with autoscaling based on CPU utilization. The team suspects the issue is related to session persistence. They have considered the following options: A) Switch to an internal TCP/UDP load balancer with session affinity; B) Enable sticky sessions (session affinity) on the existing load balancer; C) Move session storage to a centralized service like Memorystore; D) Increase the instance size and disable autoscaling. Which solution permanently resolves the issue while maintaining scalability and fault tolerance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Move session storage to a centralized service like Memorystore
Option D is correct because storing session data in a centralized service like Memorystore (Redis) decouples session state from individual Compute Engine instances. This ensures that any instance in the managed instance group can serve any user request without losing session data, even as the MIG autoscales up or down. This approach permanently resolves the issue while maintaining scalability and fault tolerance, as Memorystore provides a highly available, in-memory data store that persists across instance lifecycle events.
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.
✗
Switch to an internal TCP/UDP load balancer with session affinity
Why it's wrong here
Internal load balancer is for internal traffic, and session affinity still loses sessions if the instance fails.
✗
Increase the instance size and disable autoscaling
Why it's wrong here
This eliminates scalability and still does not protect against instance failure.
✗
Enable sticky sessions (session affinity) on the existing load balancer
Why it's wrong here
Sticky sessions only route requests to the same instance, but if the instance is replaced, sessions are lost.
✓
Move session storage to a centralized service like Memorystore
Why this is correct
Centralized session storage decouples sessions from instances, ensuring persistence across scaling and failures.
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 think sticky sessions (session affinity) alone will fix session persistence, but they overlook that autoscaling and instance failures still cause data loss when sessions are stored locally—only a centralized external store like Memorystore provides true persistence and fault tolerance.
Detailed technical explanation
How to think about this question
Under the hood, HTTP load balancers with session affinity use a hash of the client IP or a cookie to route requests to the same backend instance, but this does not replicate session data across instances. When a MIG autoscales down, instances are terminated, and any in-memory session data is lost. Memorystore (Redis) acts as a distributed cache that all instances can access via a private IP, using the Redis protocol (TCP port 6379). This pattern is often called 'stateless application design' and is a best practice for cloud-native architectures, as it allows the application to scale horizontally without stateful dependencies on individual VMs.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this ACE question in full detail.
Planning and configuring a cloud solution — This question tests Planning and configuring a cloud solution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Move session storage to a centralized service like Memorystore — Option D is correct because storing session data in a centralized service like Memorystore (Redis) decouples session state from individual Compute Engine instances. This ensures that any instance in the managed instance group can serve any user request without losing session data, even as the MIG autoscales up or down. This approach permanently resolves the issue while maintaining scalability and fault tolerance, as Memorystore provides a highly available, in-memory data store that persists across instance lifecycle events.
What should I do if I get this ACE 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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